No abstract

Abstract— A detailed in vitro study was made of the flavin sensitized photoinactivation of indoleacetic acid, using primarily riboflavin as sensitizer. The dependence of the quantum yield on reactant concentrations, pH, presence of oxygen, viscosity, temperature, KI concentration, and solvent was determined. The involvement of a limiting dark reaction was demonstrated, using an intermittent light technique. The results are consistent with a mechanism involving a metastable state of riboflavin as the photochemically reactive species. The calculated rate constant for intersystem crossing to this state was found to be 2.5 times 108/sec. Riboflavin, in the metastable state, is believed to oxidize indoleacetic acid to indolealdehyde, with subsequent recovery of riboflavin by autoxidation. The maximum quantum yield of the photoinactivation of IAA is 0.71, indicating a highly efficient process, approaching 100% when energy loss due to riboflavin fluorescence is taken into account. Both carotenoids and pure chlorophyll‐a were found to be inactive as sensitizers.

The ability of an exogenous long-chain unsaturated fatty acid (linolenic acid) to induce changes in the circular dichroism (C.D.) spectra of chlorophyllous systems of various levels of organization is demonstrated and attributed to its deaggregating influence. In the case of chlorophyll in solution (CCl(4) or CCl(4)-hexane), deaggregation is by direct action on the chromophore. Evidence is also given for an indirect mechanism when chlorophyll is attached to protein (e.g., in HP-700 complexes); in this case, deaggregation results from a conformational change in the protein. Interpretations are given for the differences in C.D. spectra of nonmembranous and membranous chlorophyll-containing systems. (The latter include "digitonin-isolated" system I particles, subchloroplast particles obtained by means of sonication, and specially prepared intact chloroplasts.)

the basis for our modified spiral. We also thank Ronald G. Stafford of lasl for his assistance in the preparation of the iron oxide aerosol and George W. Royer of lasl for generating the methylene blue-uranine aerosol with the lasl spinning disk generator.