Activation of the hill reaction by amines

Abstract

1. 1. Unidentified non-metal bases from plant and animal tissues, ammonia, and a number of monofunctional amines increase the rates at which ferricyanide and other oxidants are reduced by illuminated chloroplasts. The relatively polar polyfunctional amines are completely inactive. 2. 2. The amount of activation of the chloroplast reactions is a function of the concentration of the unionized amine. The reciprocal of the rate increase plotted against the reciprocal of the concentration of the amine (methylamine) gives a straight line. Moreover the action of the amine is completely reversible. However there is no evidence that any of the amine is consumed. 3. 3. The electron transport system operative in the absence of amines and the electron transport system activated by amines utilize different pathways. The amine-insensitive system is very stable below pH 7.0, is somewhat labile at pH 7.8, and does not reduce FMN at appreciable rates. The system activated by amines is very labile below pH 7.0, is fairly stable at pH 7.8, readily reduces FMN, and reduces all oxidants at rates which are several times greater than the maximum rate of the amine-insensitive system. 4. 4. The amine-activated system is closely related to the system which is activated by the presence of ADP, orthophosphate and magnesium ions: the two systems disappear simultaneously on storage of the chloroplasts; the activations are not additive if optimal amounts of amine have been used; and the presence of amines prevents the formation of ATP. 5. 5. The stoichiometry of the phosphorylating reaction and the manner in which amines might affect this reaction are discussed.