Red/far-red modulation in vitro of enzyme activity in a membrane fraction from Phaseolus aureus

In a membrane fraction isolated from hypocotyls of Phaseolus aureus Roxb. the activity of a number of enzymes was regulated by red and far-red irradiation in vitro, provided that the tissue received a brief red light treatment before extraction. Other enzymes showed no photoregulation. There were two types of photocontrol, neither of which could be detected in the solute fraction, nor in extracts from completely etiolated material. One (Type I) was a red/far-red reversible regulation of the rate of enzyme activity, depending on the light given (in vivo or in vitro) before the assay was begun. The second (Type II) was a promotion of enzyme activity by red or far-red light given during the assay. The action spectra for type II responses do not coincide with either the phytochrome absorption or difference spectra. However, the effectiveness of red and far-red was correlated with the P_fr/P ratio present at the beginning of the assay, such that far-red was more efficient at high P_fr/P and red at low P_fr/P ratios. All enzymes that were regulated involved ATP. In samples that showed enzyme regulation, small changes in fluorescence yield of tryptophan and the covalent probe Fluram (Roche) accompanied the photoconversion of phytochrome, but no fluorescence changes could be measured after briefly incubating the membrane fraction with ATP. The results indicate that light may affect the interaction of ATP with the membrane fraction.Abbreviations F far-red light - P_r and P_fr phytochrome in the red and far-red absorbing forms - P_tot total phytochrome - R red light - RNP ribonucleoprotein