| Abstract: | During the inactivation of the nucleotide-free F1-ATPase at pH 7.0, by p-fluorosulfonyl14C]benzoyl-5'-adenosine (14C]FSBA) in the presence of 20% glycerol, about 4.5 g atoms of 14C are incorporated/350,000 g of enzyme. Isolation of the subunits has shown: (a) over 90% of the incorporated label is associated with the alpha and beta subunits; (b) the amount of label incorporated into the alpha subunit is about 0.5 g atoms/mol which is nonspecifically associated with a number of tyrosine and lysine residues; (c) the amount of radioactivity incorporated into the beta subunit is about 0.9 g atoms/mol which correlates with the degree of inactivation of the enzyme and resides on a single tyrosine residue; (d) up to 2.2 mol of alpha subunit have been isolated from each mole of inactivated enzyme; and (e) about 2 mol of beta subunit have been isolated from each mole of inactivated enzyme. These results account for the incorporation of 4.5 g atoms of 14C which are incorporated/mol of ATPase during inactivation if there are three copies each of the alpha and beta subunit present in the enzyme. It has also been shown that 4-chloro-7-nitrobenzofurazan (NBD-Cl) and FSBA react with different tyrosine residues when they inactivate the ATPase. In addition, it has been shown that the ATPase inactivated with FSBA retains the capacity to bind up to 2.2 mol of 14C]ADP/350,000 g of enzyme. |
