EFFECTS OF 1,N6-ETHENOADENYLATES ON REGULATION OF PHOTOSYNTHETIC ACTIVITIES BY ADENYLATES - STUDY OF NUCLEOTIDE BINDING-SITES ON CHLOROPLAST COUPLING FACTOR-1

Effects of 1,N6-ethenoadenylates (.epsilon.-adenylates) were tested on phosphorylation, and electron transport under phosphorylation, arsenylation and quasi-arsenylation (stimulation of electron transport in the presence of ATP, AMP and arsenate) conditions in isolated spinach chloroplasts. .epsilon.-ATP as well as ATP partially inhibited ferricyanide reduction through binding to the chloroplast coupling factor 1 with an apparent dissociation constant (Kdapp) of around 50 .mu.M, which was remarkably larger than that for ATP (about 2 .mu.M). .epsilon.-ATP at below 500 .mu.M had no effect on phosphorylation but inhibited quasi-arsenylation in competition with ATP with an apparent inhibition constant (Kiapp) of around 60 .mu.M. .epsilon.-ADP as well as ADP partially inhibited ferricyanide reduction with a Kdapp value close to that for .epsilon.-ATP. .epsilon.-ATP was phosphorylated (the apparent Michaelis constant, Kmapp = 80 .mu.M) accompanying stimulation of ferricyanide reduction to the magnitude predicted (P/.DELTA.e = 1). .epsilon.-ADP-arsenylation was also detected by stimulation of ferricyanide reduction. .epsilon.-AMP alone caused little inhibition of ferricyanide reduction as AMP, but competitively depressed the electron transport inhibition by ADP and ATP with a Kiapp value of around 200 .mu.M. .epsilon.-AMP was not effective for ADP phosphorylation but inhibited stimulation due to quasi-arsenylation coupling in competition with AMP (Kiapp = 150 .mu.M). Among the possible combinations of adenylates and .epsilon.-adenylates for quasi-arsenylation, only [ATP+AMP] could couple with the energy transduction mechanism. Based on the specificity of binding sites to adenylates and .epsilon.-adenylates, an attempt was made to distinguish at least 4 (2 pairs) kinds of binding sites (at least 6 sites in toto) on the chloroplast coupling factor 1 for photosynthetic energy transduction. When 1 pair of sites is occupied by the designated adenylates or .epsilon.-adenylates (allosteric effectors), the coupling factor is thought to be in a conformation for coupling with the energy transduction mechanism in the presence of phosphate or arsenate.