Evidences for physically different catalytic and regulatory nucleotide binding sites on the chloroplast H(+)-ATPase.

Abstract

Chloroplast thylakoids which were incubated with pyridoxal-5-phosphate (PLP) in the dark, exhibit a slower ADP-binding curve in the light and lack the rapid initial phase of rebinding of loosely bound nucleotides upon de-energetization. The [14C]NBD binding pattern in subunits of PLP-modified thylakoids is reduced to that one found if ADP was present in the modification step. The [14C]NBD binding pattern in subunits of activated and successive PLP-modified CF1 is reduced to that one found in the latent enzyme. As in the latent (not activated) ATPase Lys beta 359 is modified by PLP, we conclude that this amino acid residue belongs to a regulatory binding site which binds ADP tightly upon de-energetization and releases it upon energetization. In the activated enzyme, however, the modified residue is related to a 9 kDa peptide in beta, which contains the conserved lysine 178. This site is proposed to be a catalytic one.