A new non-photoreducible protochlorophyll(ide-)-protein: P-649--642 from cucumber cotyledons: NADPH mediation of its transformation to photoreducible P-657--650.
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Chlorophyll↗
Biomedical subjects
C Sironval
Publications and source records attributed to C Sironval.
The dimerization of protochlorophyll pigments in non-polar solvents.
The infrared, visible and nuclear magnetic resonance spectra of protochlorophyll a and vinylprotochlorophyll a in dry non-polar solvents (carbon tetrachloride, chloroform, cyclohexane) are presented and interpreted in terms of dimer interaction. The infrared spectra in the 1600-1800 cm-1 region clearly show the existence of a coordination interaction between the C-9 ketone oxygen function of one molecule and the central magnesium atom of another molecule. Infrared spectra in the OH stretching region (3200-3800 cm-1) provide a valuable test of the water content in the samples. The analysis of the absorption and circular dichroism spectra of protochlorophyll a and vinylprotochlorophyll a in carbon tetrachloride demonstrates the existence of a monomer-dimer equilibrium in the concentration range from 10(-6) to 5.10(-4) M. The dimerization constants are (6 +/-2).10(5)1.M-1 for protochlorophyll a and (4.5 +/-21.10(5) 1.M-1 for vinylprotochlorophyll a at 20 degrees C. The deconvolution of visible spectra in the red region has been performed in order to obtain quantitative information on the dimer structure. Two models involving a parallel or a perpendicular arrangement of the associated molecules are considered. From 1H NMR spectra, it appears that the region of overlap occurs near ring V, in agreement with the interpretation of the infrared spectra.
Chemical Phenomena↗
Acetabulaira mediterranea: circadian rhythms of photosynthesis and associated changes in molecular structure of the thylakoid membranes.
Acetabularia mediterranea algae, grown in three different light-dark regimes, were frozen in liquid nitrogen at c.t.(1) 0 and c.t. 6 and a record made of 77 degrees K fluorescence emission spectra of their chloroplasts. Algae grown under LD cycles exhibited a clear circadian rhythm of oxygen production. The low temperature fluorescence emission spectrum at c.t.0 was different from that at c.t.6 and this difference was increased by submitting the algae to successive "freeze-thaw" treatment. Similar results were obtained in DD, and the photosynthesis rhythm remained fully expressed. Algae grown in LL, where no rhythm of photosynthesis could be detected in the samples because there is a great individual variability in period lenght under these conditions, exhibited a similar difference in their low temperature flourescence emission spectra between c.t.0 and c.t.6. We conclude that the circadian rhythm in low-temperature fluorescence emission of the chloroplasts in Acetabularia is related to the circadian rhythm in photosynthesis.
Acetabularia↗