QUANTUM YIELDS FOR LASER PHOTOCYCLIZATION OF BILIRUBIN IN THE PRESENCE OF HUMAN SERUM ALBUMIN. DEPENDENCE OF QUANTUM YIELD ON EXCITATION WAVELENGTH

The quantum yield for laser photocyclization of bilirubin to lumirubin in the presence of human serum albumin (phi LR) was measured at five monochromatic excitation wavelengths in the range 450-530 nm. Solutions used were optically thin throughout the wavelength range and precautions were taken to exclude contributions from photocyclization of bilirubin XIII alpha impurities. The values obtained (7.2-18 x 10(-4] were lower than those previously reported and showed the following wavelength dependence: 457.9 less than 488.0 less than 501.7 less than 514.5 approximately equal to 528.7. However, the rate of lumirubin formation, normalized to constant fluence, decreased with wavelength over the same wavelength range and no evidence was found that photoisomerization of bilirubin to lumirubin is faster with green (514.5 or 528.7 nm) than with blue (457.9 or 488.0 nm) light. The stereoselectivity of the configurational isomerization of bilirubin to 4Z,15E and 4E,15Z isomers also was studied. This reaction became less regioselective for the 4Z,15E isomer with increasing wavelength. The observed wavelength dependence of phi LR and of the [4E,15Z]: [4Z,15E] ratio at photoequilibrium are consistent with an exciton coupling model in which intramolecular energy transfer can occur between the two pyrromethenone chromophores of the bilirubin molecule in the excited state. Relative rates of lumirubin formation in vivo at different excitation wavelengths and constant fluence were estimated for different optical thicknesses and for different skin thicknesses. These estimates suggest that the recently reported clinical equivalence of blue and green phototherapy lights probably reflects the marked variation of skin transmittance with wavelength more than wavelength-dependent photochemistry. The calculations also indicated that the optimal wavelength for phototherapy is probably on the long wavelength side of the bilirubin absorption maximum.     

PHOTOREDUCTION OF CYTOCHROME b551 OF PARTIALLY PURIFIED NEUROSPORA NITRATE REDUCTASE VIA ITS INTERNAL FLAVIN

Abstract— Nitrate reductases (NR) from NR-normal Neurospora crassa mutant albino band and from NR-defective mutantsnit–1 andnit–3 were isolated and partially purified in order to test the photo-reducibility of their cytochrome b ₅₅₇ via the NR-internal FAD. Photoreducibility with blue light of the isolated enzyme was observed as absorbance increase at 423, 524 and553–557 nm. It was independent of NADPH-nitrate reductase activity and could be induced if the dissociable FAD was not lost in the isolation procedure. The photoreduction of cytochrome b ₅₅₇ was readily reversible due the high autoxi-dation rate of this cytochrome. Therefore, anaerobic conditions are required for photoreduction with low light intensities. If aerobic conditions are applied, high intensities become necessary to overcome the simultaneous cytochrome h₅₅₇ oxidation.     

Equal-quantum action spectra indicate fluence-rate-selective action of multiple photoreceptors for photomovement of the thermophilic cyanobacterium Synechococcus elongatus

Unicellular thermophilic cyanobacterium Synechococcus elongatus displayed phototaxis on agar plate at 55 degrees C. Equal-quantum action spectra for phototactic migration were determined at various fluence rates using the Okazaki Large Spectrograph as the light source. The shapes of the action spectra drastically changed depending on the fluence rate of the unilateral monochromatic irradiation: at a low fluence rate (3 mumol/m2/s), only lights in the red region had significant effect; at a medium fluence rate (10 mumol/m2/s), four major action peaks were observed at 530 nm (green), 570 nm (yellow), 640 nm (red) and 680 nm (red). At high fluence rates (30-90 mumol/m2/s), the former two peaks remained, while red peaks at 640 nm and 680 nm disappeared and, interestingly, an action peak around 700-740 nm (far-red) newly appeared. These results indicate that two or more distinct photoreceptors are involved in the phototaxis and that suitable photoreceptors are selectively active in response to the stimulus of light fluence rates. Far-red or red background lights irradiated vertically from above drastically inhibited phototaxis toward red light or far-red light, respectively. These results indicate involvement of some phytochrome(s).     

THE SENSORY PHOTORECEPTORS OF Halobacterium halobium REVISITED: ACTION SPECTRA and INFLUENCE OF BACKGROUND LIGHT*

Abstract– Action spectra of the light-dependent behavior of Halobacterium and the effect of background light have been measured with regard to the current hypothesis of Spudich and Bogomolni [Nature 312 ,509–513 (1984)], which proposes sensory rhodopsin I (sRI₅₈₇) to be the receptor for long-wavelength light, and its photoproduct S₃₇₃ to be the receptor for UV light. The action spectrum shows three maxima for attractant responses (prolonged swimming intervals) at 565, 590, and 610 nm, and two maxima for repellent responses (shortened intervals) at 370 and 480 nm. The latter is assigned to sensory rhodopsin II (P-480). All peaks are red-shifted after substitution of the endogeneous retinal by 3, 4-dehydroretinal. The peaks at 590 and 610 nm are suppressed by long-wavelength background light. Ultraviolet background light converts all attractant peaks into repellent peaks. The response at 370 nm is strongly activated by visible background light, the maximal effect occurring with 510 nm. The activated state declines with a half-life of about 1.2 s. In a growing culture, full sensitivity to UV and blue light is restored about 10 h earlier than sensitivity to long-wavelength light. Some of the results cannot easily be explained by the sRI₅₈₇/S₃₇₃ hypothesis. Explanations for the three maxima in the long-wavelength range and for the maximal activation of the UV response by 510 nm light are discussed.     

LOW TEMPERATURE ABSORBANCE AND FLUORESCENCE SPECTROSCOPY OF THE PHOTOACTIVE YELLOW PROTEIN FROM Ectothiorhodospira halophila

A simplified procedure was developed to purify the photoactive yellow protein (PYP) from Ecrorhiorhodospira halophila. Specific antibodies were used to follow the distribution of PYP through the separate purification steps. Low temperature absorbance and fluorescence characteristics of this photoactive protein were investigated. The absorbance spectrum of PYP in 67% (vol/vol) glycerol peaked at 449 and 447 nm, at room-and liquid nitrogen temperatures, respectively. It sharpened significantly upon cooling to 77 K and displayed fine-structure on the blue side of its absorbance maximum, with a spacing of 25 nm. At room temperature PYP fluoresced with a quantum yield of approximately 3.5 times 10^?-³ an emission maximum of 495 nm. Maximal excitation occurred at 457 nm, 10 nm red-shifted with respect to the absorbance maximum. At -low temperature the excitation maximum remained unaltered but maximal emission shifted significantly to the blue (to 482 nm). The quantum yield of fluorescence increased to 0.07 at this temperature. Illumination of PYP at low temperature with light from the visible part of the spectrum of electromagnetic radiation induced pronounced changes in its absorbance and fluorescence characteristics. At least two new stable intermediates were formed: one highly fluorescent, with an excitation maximum at 430 nm; additionally, a non-fluorescent red-shifted intermediate with an absorbance maximum at 490 nm. The amount formed of these two intermediates depended strongly on the wavelength of actinic illumination. In combination, these data underline the spectroscopic similarities between PYP and the retinal-containing chromoproteins that are present in Halobacterium halobium.     

Phototaxis in the ciliated protozoan Ophryoglena flava: dose-effect curves and action spectrum determination

The sensitivity of positive phototactic orientation of cells of the ciliated protozoan Ophryoglena flava has been measured for white light, broad-band blue and red light, and narrow-band monochromatic light, using a laboratory-developed computer aided system. The white-light fluence rate-response curve shows that there is no negative phototaxis in the fluence rate range investigated (0-15 W/m2) and no adaptation phenomena; it is very well fitted by a hyperbolic function; the fluence rate curves under broad band blue and red light (full width at half maximum, FWHM= 100 nm) can be fitted by the same model. The saturation level is, within experimental errors, the same for the three curves, indicating that there are no chromaticity effects and that if there is more than one photoreceptor pigment, they act independently of each other. The fluence rate-response curves determined under narrow band monochromatic light (FWHM = 10 nm) can also be fitted by the same model and show, within experimental errors, the same saturation level. An action spectrum for positive phototaxis at 10-nm intervals has been calculated from fluence rate-response curves: it shows three maxima, at 420, 540 and 590 nm. This action spectrum is significantly different from the ones for photomotile responses in Blepharisma japonicum, Stentor coeruleus and Chlamydodon mnemosyne, whereas it resembles the ones of Paramecium bursaria and Fabrea salina.     

BLUE and NEAR ULTRAVIOLET REVERSIBLE PHOTOREACTION IN THE INDUCTION OF FUNGAL CONIDIATION

Abstract— The effects of blue light and near UV light on the induction of conidiation in the fungus, Aliernuriu tomato, were investigated. Induction of conidiation was repeatedly controlled by alternating doses of near UV light and blue light. When the final light was near UV, conidiation was induced and conidia developed in the following darkness; when it was blue, the induction of conidiation was suppressed. When conidiation was induced by irradiation with a light mixed with near UV and blue, not only the time lag for inducing conidiation but also the amount of conidia formed were regulated by the fluence rates of both those lights.
Thus, 'mycochrome' is considered to function as a photoreceptor system in the induction of conidiation of this fungus.     

Melatonin Mediates Monochromatic Light‐induced Insulin‐like Growth Factor 1 Secretion of Chick Liver: Involvement of Membrane Receptors

Monochromatic lights influenced the proliferation and differentiation of skeletal satellite cells in broilers by the enhancement of insulin‐like growth factor 1 (IGF‐1) secretion. However, whether melatonin (MEL)‐mediated monochromatic lights influenced the IGF‐1 secretion remains unclear. Newly hatched broilers, including intact, sham operation and pinealectomy groups, were exposed to blue (BL), green (GL), red (RL) and white light (WL) from a light‐emitting diode system for 14 days. The results showed that GL effectively promoted the secretion of MEL and IGF‐1, the expression of proliferating cell nuclear antigen and MEL receptor subtypes Mel1a, Mel1b and Mel1c in the liver compared to BL and RL in vivo. Moreover, those was a positive correlation between MEL and IGF‐1 (r = 0.834). After pinealectomy, however, these parameters declined, and there were no differences between GL and other monochromatic light treatments. In vitro, exogenous MEL increased hepatocyte proliferation and IGF‐1 secretion. Meanwhile, the MEL enhancements were suppressed by prazosin (selective Mel1c antagonist), followed by luzindole (nonselective Mel1a/Mel1b antagonist), but not suppressed by 4‐phenyl‐2‐propionamideotetralin (selective Mel1b antagonist). These findings demonstrated that MEL mediated the monochromatic light‐induced secretion of IGF‐1 in chicks’ livers by Mel1c and that Mel1a may be involved in this process.     

Molecular spectroscopy study of the reaction of nucleic acids with brilliant cresol blue

The interaction of brilliant cresol blue (BCB) with nucleic acids in aqueous solution has been studied by spectrophotometry and Rayleigh light scattering (RLS) spectroscopy. Under suitable conditions, the RLS spectra of BCB changed significantly due to the presence of nucleic acids. RLS intensity of BCB at 364 nm is greatly enhanced with the addition of nucleic acids, and a new RLS peak is observed at 552 nm. This peak is about half the intensity of that at 364 nm. The results of this study show that BCB interacts with DNA possibly due to the cooperative effect of electrostatic attraction, intercalation, coordination and hydrophobic effect. Under optimum conditions, the increase of RLS at 364 nm of a BCB solution is proportional to the concentration of nucleic acids added. This result is the basis for a new RLS method for determination of nucleic acids. The linear range of ctDNA, fsDNA and yRNA is 0.12-4.70, 0.11-4.64 and 0.43-7.07 microg ml(-1), respectively.     

Wavelength-specific activation of MAP kinase family proteins by monochromatic UV irradiation

The depletion of stratospheric ozone causes related increase in UV light below about 310 nm, which significantly affects biological and ecological systems. To understand the wavelength-specific effects of UV light, Molt4 cells (human T lymphoma cells) were irradiated with a series of monochromatic UV lights and the activities of three members of the mitogen-activated protein (MAP) kinase group were examined. Extracellular signal-regulated kinase was specifically activated within 1 min after UV irradiation in the range 320-360 nm. In contrast, P38 kinase was activated by 270-280 nm light with a peak at 1 min after irradiation. c-Jun N-terminal kinase activation was observed in a narrow range of UV light with a sharp peak at 280 nm occurring in 10 min. JNK translocated from the cytosol to the nucleus upon irradiation, while P38 remained in the cytosol even after UV irradiation. The activation of three MAP kinases was prevented by antioxidant reagents, suggesting that an oxidative signal initiates these responses. These results confirm that UV light affects various cellular functions through the activation of intracellular signaling systems including MAP kinase family proteins. However, the UV-induced activities of the separate MAP kinases show distinctly different dose, time and wavelength dependencies.     

THE PHOTOMOVEMENT OF Caenorhabditis elegans, A NEMATODE WHICH LACKS OCELLI. PROOF THAT THE RESPONSE IS TO LIGHT NOT RADIANT HEATING

Abstract— Caenorhabditis elegans adults were tested at constant temperature with 10 s periods of monochromatic light alternated with 20 s dark periods. Stimuli at effective intensities and wavelengths caused an increase in the frequency of ecclitic (phobic, avoidance) responses, which was measured as an increase in the probability of a temporary reversal in direction of movement. For monochromatic stimuli ranging from 420 to 680 nm at a constant 56 picoeinsteins s^-1 cm^-2, only those at520–600 nm elicited significant responses. At 540 nm the threshold fluence rate was approximately 30 pE s^-1 cm^-2. At saturating intensities the mean reversal probability was increased to 0.20 in 10 s from a background level of 0.12. approximately.
Because C. elegans lacks ocelli and is very sensitive to temperature, possible sources of radiant heating were considered in detail, including (a) infrared present in the stimuli, (b) absorption of light by the arena, and (c) absorption of light by a nematode pigment. All possible sources were found to cause a negligible temperature rise, on the order of or less than the natural temperature fluctuations inside the worm, 1.5 times 10^-6°C. A 2 times 10^-4°C temperature rise produced by a 1230 nm infrared stimulus had no significant effect on reversal frequency. It was concluded that the response to illumination must have been to light, and not to temperature changes.
Large, + or - 2 °C changes from the acclimation temperature caused significant increases in the background frequency of ecclitic responses (a thermoecclisis or thermoklinokinesis). However, neither the threshold nor the saturation level of light-induced responses was affected by the ± 2°C changes.     

Somatic-cell mutation induced by UVA and monochromatic UV radiation in repair-proficient and -deficient Drosophila melanogaster

Near-ultraviolet light (UVA: 320-400 nm) constitutes a major part of sunlight UV. It is important to know the effect of UVA on the biological activities of organisms on the earth. We have previously reported that black light induces somatic-cell mutation in Drosophila larvae. To investigate which wavelength of the UVA is responsible for the mutation we have now carried out a series of monochromatic irradiations (310, 320, 330, 340, 360, 380 and 400 nm) on Drosophila larvae, using the large spectrograph of the National Institute for Basic Biology (Okazaki National Research Institutes, Okazaki, Japan). Mutagenic activity was examined by the Drosophila wing-spot test in which we observe mutant wing hair colonies (spots) on the wings of adult flies obtained from the treated larvae. The induction of mutation was highest by irradiation at 310 nm and decreased as the wavelength became longer. Neither the 380 nor the 400 nm light was mutagenic. Excision repair is known to protect cells from UV damage. In the excision-repair-deficient Drosophila, the mutagenic response induced by 310 nm irradiation was 24-fold higher than that of the wild-type (7.2 +/- 1.5 spots/wing/kJ vs 0.3 +/- 0.08 spots/wing/kJ), and at 320 nm the difference of the response was 14-fold (0.21 vs 0.015 +/- 0.005). In the case of irradiation at 330 and 340 nm the difference of the response was only two-fold (at 330 nm, 6.9 +/- 2.9 x 10(-3) vs 3.1 +/- 1.1 x 10(-3) spots/wing/kJ; at 340 nm, 3.5 +/- 0.9 x 10(-3) vs 2.0 +/- 0.7 x 10(-3). These results suggest that the lesion caused in the larvae by 320 nm irradiation may be similar to the damage induced by 310 nm and that the lights of 330 and 340 nm may induce damage different from the lesions induced by shorter-wavelength lights.     

Effects of Supplementary Blue and UV-A LED Lights on Morphology and Phytochemicals of Brassicaceae Baby-Leaves

Brassicaceae baby-leaves are good source of functional phytochemicals. To investigate how Chinese kale and pak-choi baby-leaves in response to different wavebands of blue (430 nm and 465 nm) and UV-A (380 nm and 400 nm) LED, the plant growth, glucosinolates, antioxidants, and minerals were determined. Both agronomy traits and phytochemical contents were significantly affected. Blue and UV-A light played a predominant role in increasing the plant biomass and morphology, as well as the contents of antioxidant compounds (vitamin C, vitamin E, phenolics, and individual flavonols), the antioxidant activity (DPPH and FRAP), and the total glucosinolates accumulation. In particular, four light wavebands significantly decreased the content of progoitrin, while 400 nm UV-A light and 430 nm blue light were efficient in elevating the contents of sinigrin and glucobrassicin in Chinese kale. Meanwhile, 400 nm UV-A light was able to increase the contents of glucoraphanin, sinigrin, and glucobrassicin in pak-choi. From the global view of heatmap, blue lights were more efficient in increasing the yield and phytochemical levels of two baby-leaves.     

THE ACTION SPECTRA FOR UV-INDUCED SUPPRESSION OF MLR and MECLR SHOW THAT IMMUNOSUPPRESSION IS MEDIATED BY DNA DAMAGE

-Ultraviolet-B (UVB,280–320 nm) radiation can promote the induction of skin cancer by two mechanisms: damage of epidermal DNA and suppression of the immune system, allowing the developing tumor to escape immune surveillance. The mixed lymphocyte reaction (MLR) and the mixed epidermal cell lymphocyte reaction (MECLR) are commonly used methods to study the immunosuppressive effects of UVB radiation. To obtain a better understanding of the mechanism by which UVB radiation decreases the alloactivating capacity of in vitro-irradiated cells, action spectra for the MLR and MECLR were determined. Suspensions of peripheral blood mononuclear cells or epidermal cells were irradiated with monochromatic light of 254, 297, 302 or 312 nm and used as stimulator cells in the MLR or MECLR. Using dose-response curves for each wavelength, the action spectra were calculated. Both MLR and MECLR action spectra had a maximum at 254 nm and a relative sensitivity at 312 nm that was a thousand times lower than at 254 nm. Strikingly, the action spectra corresponded very closely to the action spectra that were found by Matsunaga et al. (Photochem. Photobiol. 54,403–410, 1991) for the induction of thymine dimers and (6-4)photoproducts in irradiated calf thymus DNA solutions, strongly suggesting that the UV-induced abrogation of the MLR and MECLR responses is mediated by UV-induced DNA damage. Furthermore, the action spectra for the MLR and MECLR were similar, suggesting that they share a common mechanism for UV-induced suppression.     

New Phosphors for White LEDs

White light-emitting diodes (WLEDs) have matched the emission efficiency of florescent lights and will rapidly spread as light source for homes and offices in the next 5 to 10 years. WLEDs provide a light element having a semiconductor light emitting layer (blue or UV LEDs) and photoluminescence phosphors. GaN-based highly efficient blue InGaN LEDs combined with phosphors can produce white light. These solid-state LED lamps have a number of advantages over conventional incandescent bulbs and halogen lamps, such as high efficiency to convert electrical energy into light, reliability, and long operating lifetime (about 100,000 hours). For the purpose of development of high energy-efficient white light sources, we need to produce highly efficient new phosphors, which can absorb excitation energy from blue or UV LEDs and generate emissions.In this paper, we investigate the development of blue or UV LEDs by the appropriate combination of new phosphors which can lead us to obtain high brightness white light. The criteria of choosing the best phosphors, for blue (380-450 nm) and UV (360-400 nm) LEDs, strongly depends on the absorption and emission of the phosphors. Moreover, the balance light between the light emission from blue LEDs and the yellow YAG:Ce,Gd phosphor is important to obtain white light with high color temperature. The phosphors with high efficiency which can be excited by UV LEDs are important to obtain the white light with high color rendering index.     

ACTION SPECTRA FOR INHIBITION OF HYPOCOTYL GROWTH OF WILD-TYPE PLANTS AND OF THE hy2 LONG-HYPOCOTYL MUTANT OF Arabidopsis thaliana L.

Abstract— An analysis was made by action spectroscopy, using the Okazaki Large Spectrograph, of the inhibition of hypocotyl elongation of wild-type plants and the hy2 mutant of Arabidopsis thaliana. Two day old etiolated seedlings were irradiated for 8 h with monochromatic light and left in the dark for 16 h before measurement of hypocotyl length. Spectrophotometric measurement showed that levels of phytochrome in the etiolated tissue of the hy2 mutant were less than 9% of those in the wild type. The action spectra of the wild type looked like those of high irradiance response and showed peaks at 375, 450, 625 and 725 nm, whereas the action spectra of hy2 showed only the peaks at 375 and 450 nm. Monochromatic light of wavelengths longer than 500 nm had no significant inhibitory effects on hy2 plants. Blue and UV-A light were about five times more effective in the wild type than in hy2 plants. Severe inhibitory effects were observed with UV-B light. It is concluded that inhibition of the growth of the hypocotyl involves combined actions of phytochrome and a putative blue/UV-A photoreceptor(s).     

BLUE LIGHT EFFECT ON CHLOROPHYLL FORMATION IN CHLORELLA PROTOTHECOIDES

The effectiveness of monochromatic light on chlorophyll formation over a range of 420–80 nm was examined in the regreening cells of Chlorella protothecoides in the presence of chloro-phenyl dimethylurea (CMU). An action spectrum showed two maxima with a minimum near 450 nm. At the most effective wavelength examined (444 nm), 0.2 W. m ^-2 was sufficient for half saturation. The activity of 5-aminolevulinic acid (ALA) production was examined in the greening cells under irradiation with white, blue and red light. The activity was always limited by availability of substrate, especially in the case where the greening cells were incubated with cycloheximide or transferred to darkness. Decay of the activity in these cases was delayed by provision of organic compounds such as glycine, pyruvate or glucose. The effectiveness of blue light on ALA* production observed in the presence of CMU was inferred to be brought about by the increased availability of endogenous substrates.     

MULTIPLICATIVE ACTION OF A UV-B PHOTORECEPTOR and PHYTOCHROME IN ANTHOCYANIN SYNTHESIS

Using 290-nm light, which excites only a UV-B photoreceptor, and 385- and 660-nm light, which activate only phytochrome, the fluence rate-response curves of monochromatic irradiations for anthocyanin synthesis in the first internodes of broom sorghum (Sorghum bicolor Moench, cv. Acme Broomcorn) were analyzed. Although the two photoreceptors absorbed light independently, they multiplicatively increased the action of each other. Accordingly, when the fluence rates of both wavelengths were changed together, the resulting slopes of the fluence rate-response curves of double-log plots were steep compared with the slopes obtained with the respective monochromatic irradiations. The slopes of fluence rate-response curves for monochromatic irradiations at 325 to 345 nm were steeper than those at other wavelengths. This difference was shown to be due to the multiplicative actions of both photoreceptors.     

LIGHT-CONTROLLED ADAPTATION KINETICS IN Phycomyces: EVIDENCE FOR A NOVEL YELLOW-LIGHT ABSORBING PIGMENT

When sporangiophores of the fungus Phycomyces blakesleeanus adapt from high to low fluence rate, dark adaptation (sensitivity recovery) can be accelerated by dim subliminal light [Galland et al. (1989) Photochem. Photobiol. 49, 485-491]. We measured fluence rate-response curves for this acceleration under the following conditions. After sporangiophores were initially adapted symmetrically to a fluence rate of 1 W m-2 (447 nm), they were exposed to unilateral subliminal light (subthreshold for phototropism) of variable wavelength and fluence rate, and then to unilateral test light (447 nm) of fluence rate either 10(-3) or 10(-5) W m-2. The duration of the subliminal light was chosen so that phototropism would not occur during this period. Phototropic latencies could be shortened by subliminal light that was less intense than the test light by several orders of magnitude. In experiments with the final unilateral light of fluence rate 10(-3) W m-2, the 447 nm subliminal light had a threshold (for the acceleration effect) of about 10(-11) W m-2. Yellow light of wavelength 575 nm, which itself is extremely ineffective for phototropism was extremely effective in shortening phototropic latencies in response in response to the test light. At 575 nm, the threshold was about 2 x 10(-12) W m-2. Conversely, near-UV light of wavelength 347 nm, which is highly effective for phototropism, was relatively ineffective (threshold approximately 7 x 10(-8) W m-2) in shortening the phototropic latency. Our results suggest the presence of a novel yellow-light absorbing pigment in Phycomyces that specifically regulates dark adaptation.(ABSTRACT TRUNCATED AT 250 WORDS)     

INDUCTION OF DNA-PROTEIN CROSSLINKS IN HUMAN CELLS BY ULTRAVIOLET and VISIBLE RADIATIONS: ACTION SPECTRUM

Abstract— DNA-protein crosslinking was induced in cultured human P3 teratocarcinoma cells by irradiation with monochromatic radiation with wavelengths in the range254–434 nm (far-UV, near-UV, and blue light). Wavelength 545 nm green light did not induce these crosslinks, using the method of alkaline elution of the DNA from membrane filters. The action spectrum for the formation of DNA-protein crosslinks revealed two maxima, one in the far-UV spectrum that closely coincided with the relative spectrum of DNA at 254 and 290 nm, and one in the visible light spectrum at 405 nm, which has no counterpart in the DNA spectrum. The primary events for the formation of DNA-protein crosslinks by such long-wavelength radiation probably involve photosensitizers. This dual mechanism for DNA-protein crosslink formation is in strong contrast to the single mechanism for pyrimidine dimer formation in DNA, which apparently has no component in the visible light spectrum.