Bromobimane crosslinking studies in oligomycin-sensitive ATPase from beef heart mitochondria. Mr 31 000 protein crosslinked

Using a bromobimane fluorescent label the Mr 31 000 protein band oligomycin-sensitive (OS)-ATPase from beef heart mitochondria is shown to become much intensified by 2-mercaptopropionylglycine. In the presence of 3.5 nmol/mg protein of the thiol reagent ATP—Pi exchange activity is increased by 90%. With the fluorescent crosslinking reagent dibromobimane (DB) we show that a new fluorescent peak appears between Mr 50 000 and 60 000. ATP—Pi exchange is very much decreased by DB. The results suggest that for regulation of ATP-synthetase activity sulfhydryl groups in the region of the Mr 31 000 protein(s) play an important role.