An essential arginyl residue in the soluble chloroplast ATPase.

Abstract

The photosynthetic formation of ATP in chloroplasts requires a coupling factor wtih latent ATPase activity, which has been purified to homogeneity [ 1,2] , has a molecular weight of 325 000 [ 1 ] and is made up of five different subunits [3] . Studies intended to characterize the active site(s) of the coupling factor have been carried out by chemical modification with Nethylmaleimide [4,5] , 7-chloro-4~nitrobenzo-2-oxa-I ,3diazole [6] , o-iodosobenzoate [7] ,2,2’-dithio-bis(5nitropyridine) [8,9] and trypsin treatment [6] . Inhibition of the ATPase activity of the chloroplast coupling factor by 7-chloro4-nitrobenzo-2-oxa-1,3diazole suggests the involvement of tyrosine residues in the catalytic site [6] . The participation of arginyl residues in the binding of anionic substrates or ligands in several enzymes have been shown by chemical modification with cu-dicarbonyl reagents [lo-141 . Recently, Borders et al. [lo] suggested that the adenine nucleotide binding site of creatine kinase contains an essential arginyl residue and Marcus et al. [ 1 l] found that modification of an arginyl residue of the mitochondrial ATPase, probably at the hydrolytic site, resulted in enzyme inactivation. The present paper reports the effects of an arginine-specific reagent, 2,3-butanedione in borate buffer, on the ATPase activity of the purified spinach chloroplast coupling factor. The results obtained suggest that there is one essential arginine per active site in the chloroplast ATPase. 2. Experimental