EFFECT OF SPLIT-DOSE U.V. IRRADIATION ON DIPLOID YEAST

Abstract— Recovery from sublethal damage by u.v. irradiation as measured by the split-dose technique was investigated in stationary phase populations of diploid yeast Saccharomyces cerevisiae. Ft has been found that only about 35 per cent of the irradiated population is able to undergo recovery before the first subsequent cell division. The qualitative pattern is not changed if maximum photoreactivation is allowed after the first dose. Measurements of the decay of photoreactibility show that primary photo-products are still present up to six hours after irradiation.     

INTERACTION OF ENZYME-GENERATED SPECIES WITH CHLOROPHYLL-a AND PROBES BOUND TO SERUM ALBUMINS

Abstract— The interaction of serum albumin-bound acceptors with enzyme-generated and protected triplet species was studied in two types of systems. Chlorophyll-a bound to bovine and human serum albumins is efficiently excited by enzymatically generated triplet acetone and acetaldehyde. When the Chl-a concentration is much lower than that of the albumin the interaction occurs with chlorophyll in an aggregate in which one Chl-a is surrounded by several protein molecules. When the Chl-a concentration is higher than that of the protein, the aggregate contains the proteins and fluorescent chlorophylls in a 1:1 ratio. The excess chlorophylls, although able to interact with the donors, are not fluorescent.
In another study, probes bound to various specific sites of serum albumins were used as quenchers of the enzymatically generated triplet acetone. The efficiency of quenching by all the bound probes is equal and in one case even stronger than for the free probes.
A model for the interaction of the excited species contained in the enzyme with the acceptor(s) located in the protein is proposed.
The present results provide further evidence that enzyme-generated and protected triplet carbonyl species can interact through a collisional process with acceptors bound to or constituents of macromolecules.     

EFFECT OF U.V.-IRRADIATION ON SEDIMENTATION BEHAVIOR OF VARIOUS PROTEINS

Abstract— Moderate u.v.-doses (2537 Å) sufficient to reduce enzymatic activities of native enzymes up to about 90 per cent, in general do not produce measurable amounts of smaller dialyzable fragments.
The disappearance of the original boundary in sedimentation diagrams is mostly due to the formation of rapidly sedimenting polydispersed material. Generally the sedimentation constants of the native proteins are not significantly changed. The boundaries, however, often loose their symmetry. The quantum yields for the disappearance of the original boundaries are roughly inversely proportional to the molecular weights. The number of molecules disappearing from the main peak is smaller than the number of molecules inactivated by a given dose. The data indicate that ultracentrifugation provides no satisfactory method for separation of native molecules from the damaged and inactivated. Proteins with labile quaternary structures (e.g. thyroglobulin or hemocyanine) which tend to dissociate under very mild conditions show an enhanced dissociation after u. v.-irradiation.     

DIFFUSE SPECTRAL REFLECTANCE MODIFICATION OF SKIN BY U.V. IRRADIATION

Abstract— Irradiation of guinea pig skin in vivo with light shorter than 300 nm produced a significant decrease in 330–400 nm reflectance. A similar decrease in reflectance was seen by irradiation of excised guinea pig and human skin. Chemical or physical vasodilation had no effect on the 240–400 nm reflectance. Irradiation of guinea pig skin in vivo with light longer than 300 nm produced no change in 330–400 nm reflectance unless photosensitized with 8-MOP. U.V. irradiation of skin (in the presence of suitable endogenous or exogenous photo-sensitizers) may result in the formation of new products that effectively absorb 330–400 nm photons.     

EFFECT OF NEAR-ULTRAVIOLET IRRADIATION ON PLANARIA*

Abstract— Near-UV radiation in the UV-B range prevented regeneration of segments of the turbellarian worm, Planaria. and reduced survival of intact animals as a direct function of the fluence supplied. Survival was photoperiod dependent suggesting dark-repair capacity. Near-UV radiation induced melanogenesis     

聚乙烯序态结构对辐照交联的影响

聚乙烯的形态结构明显的影响辐照交联。结晶形态结构越不完整,结晶度越低,界面越多,则形成分子间的交联越多。 通过聚乙烯球晶的拉伸、腐蚀和熔融时形态的变化,可以认为,在所有序态结构的界面上均可产生分子间的交联,而且优先在片层之间产生。 当分子间交联使凝胶量达92％以上时,随辐照剂量的增加,结晶度和晶粒变小;折光指数和密度随之增加;而分子链段取向却随之降低。     

辐照亚硫酸纸浆结晶度的研究

<正> 纤维素分子中含有大量的羟基,易形成氢键,是结晶性很高的聚合物,无论在研究工作和工业生产中,这一性质都受到高度重视。纤维素在辐照场中的结晶行为,也是被研究的重点。从已发表的研究结果看,辐照纤维素的结晶行为有很大的差别,据有关文章报道,在γ射线和电子束射线的辐照场中,纤维素的结晶结构没有变化。例如,美国     

辐照温度对聚芳醚酮辐射交联行为的影响

<正> 可溶性含酚酞侧基聚芳醚酮(PEK-C)是一种新型的具有耐高温、耐水解、耐化学腐蚀、自润滑性能的工程塑料,它具有如下结构:     

PHOSPHORESCENCE LIFETIME STUDIES OF INTERACTIONS BETWEEN SERUM ALBUMINS AND SODIUM DODECYL SULFATE

Binding of sodium dodecyl sulfate (SDS) to bovine serum albumin (BSA) and human serum albumin (HSA) in aqueous solutions at room temperature induces significant changes in the phosphorescence lifetime of tryptophan (Trp) residues. A steep rise of the phosphorescence lifetime from 1.9 ms to 10.0 ms for BSA and from 1.9 ms to 5.5 ms for HSA is observed when the total SDS concentration increased from 0.0 mM to 0.22 mM at 1 mg/mL protein concentration. As the total SDS concentrationis further inccreased to 2.2 mM, a slower increase in the phosphorescence lifetime is observed, from 10.0 ms to 19.5 ms for BSA and from 5.5 ms to 7.2 ms for HSA. It appears that the phosphorescence lifetime modifications are mainly due to an increase of protein matrix rigidity around Trp residues. The observed differences (between HSA and BSA) allow us to distinguish the contribution of the two Trp residues to the BSA phosphorescence.     

PHOTOCHEMICAL-LIKE DESTRUCTION OF TRYPTOPHAN IN SERUM ALBUMINS INDUCED BY ENZYME-GENERATED TRIPLET SPECIES

Abstract —Human and bovine serum albumin quench enzyme-generated acetone phosphorescence ( K _sv= ca . 10⁴ M ¹). Concomitantly, these proteins are altered as shown by diminished tryptophan absorption at 280 nm, appearance of products of the formylkynurenine type (_max= ca . 320 nm) and disappearance of tryptophan fluorescence. These alterations—which are similar to those induced photochemically—were also observed with serum albumins exposed to enzyme-generated triplet acetaldehyde. On the other hand, triplet acetone generated by the thermolysis of tetramethyldioxetane failed to induce alterations. Presumably energy transfer occurs from the enzyme-generated triplet species to tryptophan group(s) in the serum albumin associated with the acting enzyme. The detailed mechanism is, however, not yet understood.     

电子辐射对聚乙烯高弹性性能的影响

<正> 由于超高模量聚乙烯(Ultra-High Modulus Polyethylene,简称UHMPE)纤维可望作绳索和复合材料等工程材料而在工程上获得广泛应用,面临的一个重要任务就是设法尽可能地改善其力学性能,已有几篇研究论文报道了不同拉伸比,不同分子量和γ辐射对UHMPE结构和性能的影响,这些方法都在不同程度上改善了纤维的性能。本实验则研究了各种不同剂量的电子辐射对UHMPE高弹性性能及结构的影响。至于电     

γ-射线辐照对尼龙6纤维结构的影响

<正> 过去的大多数研究表明,高能射线辐照会引起聚乙烯及聚丙烯等稀烃类聚合物分子链交联及降解,而且会导致结晶度下降。张利华等人最近的研究表明,对于尼龙1010塑料,仅当辐照剂量高到一定程度后,辐照才会破坏结晶。此外,Stowe等人曾经研究过近紫外线对尼龙66纤维结构的影响,结果表明,在空气气氛中的近紫外辐照主要导致尼龙66纤维降解,并使纤维结晶度提高。有关高能射线辐照对高度取向的合成纤维结构及性能的影响的研究尚不多见。本工作将讨论γ-射线对于尼龙6纤维结构的影响。     

THE EFFECT OF IRRADIATION ON THE POLYETHERKETONE WITH CARDO GROUP

The effects of irradiation on the polyetherketone with cardo group (PEK-C) were studied. It was found that PEK-C can be crosslinked by irradiation under vacuum, while degradation reaction occurred in PEK-C at room temperature in the presence of air. Moreover. it was also found that Ts value of the crosslinked PEK-C at high temperature is higher than that at room temperature in the case of the same gel content, whose value is about 8℃higher than that of unirradiated PEK-C. The gelation dose of PEK-C at 300℃under vacuum is 1.5×10~4 Gy, which is about hundred times smaller than that at room temperature.     

EFFECT OF UV IRRADIATION ON LETHAL INFECTION OF MICE WITH Candida albicans

Exposure of mice to UV radiation inhibits the induction and elicitation of the delayed-type hypersensitivity (DTH) response to Candida albicans. To determine whether UV irradiation also affects the pathogenesis of systemic C. albicans infection, C3H mice were exposed to a single dose of 48 kJ/m² UV-B radiation from FS40 sunlamps 5 days before or 5 days after sensitization with formalin-fixed C. albicans and challenged intravenously (i.v.) with a lethal dose of viable fungi 6 days after sensitization (11 or 1 days after UV irradiation). Exposing unsensitized mice to UV radiation 11 days before lethal challenge had no effect on survival, but the survival time of mice exposed to UV radiation 1 day before challenge was reduced by more than 50%. In the latter group, decreased survival time correlated with persistence of C. albicans in the brain and progressive growth of C. albicans in the kidneys. Sensitization of unirradiated mice with formalin-fixed C. albicans extended their survival time following lethal i.v. challenge with viable C. albicans. Exposing the mice to UV radiation 5 days before sensitization did not abrogate this beneficial effect of sensitization on survival, even though it significantly reduced the DTH response. Thus, immunity to systemic infection did not depend on the ability of the mice to exhibit a DTH response to C. albicans. The beneficial effect of sensitization on survival after lethal infection was abrogated, however, in mice exposed to UV radiation 1 day before lethal challenge with C. albicans. Furthermore, these mice were unable to contain the progressive growth of C. albicuns in the kidneys, in contrast to sensitized, unirradiated mice. The induction of cutaneous inflammation with turpentine had no effect on the survival rate of mice lethally infected with C. albicans, suggesting that inflammation alone is not sufficient to decrease the survival time of C. albicans-infected mice.     

ENHANCED SUSCEPTIBILITY TO HPD-SENSITIZED PHOTOTOXICITY AND CORRELATED RESISTANCE TO TRYPSIN DETACHMENT IN SV-40 TRANSFORMED IMR-90 CELLS

Abstract— The response of a normal human cell strain, IMR-90 and a line derived from it by SV40 transformation were compared after treatment in vitro with hematoporphyrin derivative (HPD) and red light. Transformed cells were inactivated at a significantly higher rate than normal cells when assayed by clonogenic survival. Co-treatment with HPD and light also induces cellular resistance to enzymatic cleavage by trypsin; transformed cells exhibit a greater resistance than the normal cells to detachment from the growing surface. These data indicate that transformed cells may possess intrinsic characteristics that render them more sensitive than normal cells to HPD-induced phototoxicity and that the plasma membrane may be the site of differential toxicity.     

CHLORPROMAZINE PHOTOSENSITIZATION—I. EFFECT OF NEAR-UV IRRADIATION ON BACTERIOPHAGES SENSITIZED WITH CHLORPROMAZINE

Abstract— Both DNA bacteriophage and RNA bacteriophage were inactivated when they were irradiated with near-UV light (black light) in the presence of chlorpromazine. The far-UV sensitive mutants of T4D, i.e. T4D v , T4D px and T4D y , were no more sensitive to near-UV light plus chlorpromazine than the wild type. Electron microscopic observations showed that adsorption of T4D was greatly influenced by the treatment. The present results may indicate that the inactivation of T4D is due to the loss of adsorption caused by impairment in the tail or the tail fiber protein rather than the inactivation of DNA.