THE INTERACTION OF TENTOXIN WITH CF1 AND CF1-EPSILON ISOLATED FROM SPINACH CHLOROPLAST

Different HPLC techniques were applied to investigate the interaction of the cyclic tetrapeptide tentoxin with the chloroplast coupling factor 1 (CF1) prepared from spinach. Tentoxin bound stoichiometrically 1:1 with the CF1, although dissociation of the epsilon-subunit might correlate with an additional binding revealing a second, low-affinity binding site. Tentoxin binding did not depend on the presence of ADP and did not change the number of binding sites for ADP on the CF1, indicating a non-competitive binding. Binding of the natural derivative, dihydrotentoxin, was indirectly demonstrated. The calcium- and the magnesium-dependent ATPase activities of the CK were strongly inhibited at low tentoxin concentration whereas at concentrations of 5 mu M and above they were increasingly stimulated. The mechanism of action and the binding site of tentoxin on the beta-subunit are discussed and a new hypothesis is presented.