EFFECT OF LIGHT ON OSCILLATIONS OF ENZYME ACTIVITY DURING PHOTOMORPHOGENESIS IN CHENOPODIUM RUBRUM L.

An approach to determine the photomorphogenic effect of light (white or continuous far-red) on the development of rhythmic enzyme activity in Chenopodium rubrum L. is described. Previous results, obtained from mature seedlings grown in white light, demonstrated stable oscillations with periods ranging between 12 and 15 h for all of the enzymes tested. The present results, obtained during deetiolation, were complicated by the presence of a higher frequency component with a period of about 6 h. When the various oscillating components were defined, the analysis showed: (1) the enzymes of the Krebs cycle (malate and isocitrate dehydrogenase), the closely associated glutamate dehydrogen-ase, and the glycolytic pathway ((NAD) glyceraldehyde-3-phosphate dehydrogenase) had a dominant period in the range of 12–15 h, (2) those of the oxidative pentose phosphate pathway were either weakly circadian (glucose-6-phosphate dehydrogenase) or apparently arhythmic (6-phosphogluconate dehydrogenase), (3) the (NADP) glyceraldehyde-3-phosphate dehydrogenase from the Calvin cycle was circadian when kept in continuous darkness but becomes 15 h when placed in light, and (4) only the Calvin cycle enzyme is affected by light in the level of its activity and in its oscillatory behavior.     

PHOTOCHEMICAL REACTION BETWEEN PROTEIN AND NUCLEIC ACIDS: PHOTOADDITION OF TRYPTOPHAN TO PYRIMIDINE BASES*1

Abstract— The photochemical interactions between tryptophan and nucleic acid bases were studied. When aqueous solutions of tryptophan were irradiated (Λ > 260 nm) at neutral pH in the presence of each of the nucleic acid bases, pyrimidine bases but not purine bases were altered. Air was found to decrease the rate of reaction. Two classes of photoproducts were isolated by thin layer and ion-exchange chromatography and partially characterized. One was the dihydro-pyrimidine forms of the base (see Reeve and Hopkins, 1979) and the other consisted of tryptophan-pyrimidine photoadducts. Four tryptophan-uracil and two tryptophan-thymine adducts each with a 1:1 molecular stochiometry were found. Spectroscopic measurements and a positive reaction with Ehrlich's reagent indicate that the indole nucleus remained intact, but that the pyrimidine base was reduced at the 5, 6 double bond. The absence of a positive ninhydrin reaction and the effect of pH on the quantum yield of the photoadduct formation indicated that the ionized a-amino acid group of tryptophan was involved in photoadduct formation. Indole derivatives lacking an a-amino group were also found to form photoadducts with pyrimidine bases. The experimental results are consistent with a reaction mechanism involving tryptophan excitation to the first excited singlet state as the initial event. Radical scavenging experiments indicate that tryptophan free radicals, formed by electron dissociation from the excited state, react with the ground state pyrimidine.     

Facile and purification free synthesis of peptides utilizing ROMPgel- and ROMPsphere-supported coupling reagents

5-Norbornene-2-carboxaldehyde and norbornadiene were respectively converted into norbornene derivatives functionalized with fluoroformamidinium hexafluorophosphate and 2-bromo-N-methylpyridinium tetrafluoroborate residues. Both these norbornene monomers were ring opening metathesis polymerized or graft copolymerized onto polystyrene cores to produce ROMPgel and ROMPsphere peptide-coupling reagents. These were used to prepare hindered amides, dipeptides and tripeptides with minimal purification in parallel arrays.     

Nanometal surface energy transfer in optical rulers, breaking the FRET barrier

Optical-based distance measurements are essential for tracking biomolecular conformational changes, drug discovery, and cell biology. Traditional Forster resonance energy transfer (FRET) is efficient for separation distances up to 100 A. We report the first successful application of a dipole-surface type energy transfer from a molecular dipole to a nanometal surface that more than doubles the traditional Forster range (220 A) and follows a 1/R(4) distance dependence. We appended a 1.4 nm Au cluster to the 5' end of one DNA strand as the energy acceptor and a fluorescein (FAM) to the 5' end of the complementary strand as the energy donor. Analysis of the energy transfer on DNA lengths (15, 20, 30, 60bp), complemented by protein-induced DNA bending, provides the basis for fully mapping the extent of this dipole surface type mechanism over its entire usable range (50-250 A). Further, protein function is fully compatible with these nanometal-DNA constructs. Significantly extending the range of optical based methods in molecular rulers is an important leap forward for biophysics.     

Enantioselective synthesis of the AB-ring system of the antitumor antibiotic tetrazomine

The synthesis of the 1,2,3,4-tetrahydroisoquinoline moiety of tetrazomine was accomplished in 18 steps and in 3% overall yield from commercially available o-anisaldehyde. The reaction sequence utilizes a Sharpless asymmetric dihydroxylation to install the stereocenter and an intramolecular Friedel--Crafts hydroxyalkylation with an N-protected 2-oxo-acetamide to close the heterocyclic ring.     

Harnessing Plasticity in an Amine-Borane as a Piezoelectric and Pyroelectric Flexible Film

We demonstrate that trimethylamine borane can exhibit desirable piezoelectric and pyroelectric properties. The material was shown to be able operate as a flexible film for both thermal sensing, thermal energy conversion and mechanical sensing with high open circuit voltages (>10 V). A piezoelectric coefficient of d₃₃≈10–16 pC N⁻¹, and pyroelectric coefficient of p≈25.8 μC m⁻² K⁻¹ were achieved after poling, with high pyroelectric figure of merits for sensing and harvesting, along with a relative permittivity of 6.3.