Effect of dicyclohexylcarbodiimide on unisite and multisite catalytic activities of the adenosinetriphosphatase of Escherichia coli

The inhibitory effect of dicyclohexylcarbodiimide (DCCD) on the activity of the adenosine-triphosphatase of Escherichia coli (ECF1) has been examined in detail. DCCD reacted with ECF1 predominantly in beta subunits with a maximum of 2 mol of reagent per mole of ECF1 being incorporated in these subunits. Ninety-five percent inhibition of steady-state or multistate ATPase activity required incorporation of 1 mol of DCCD per mole of enzyme into beta subunits. Seventy-five percent inhibition of the initial rate of unisite catalysis was only obtained after incorporation of 2 mol of DCCD per mole of ECF1 into beta subunits. Analyses of the kinetics of unisite catalysis and nucleotide binding experiments both indicate that DCCD binds outside the substrate ATP binding site. Inhibition by this reagent appears to be due in part to an effect on the catalytic sites but mainly to the blocking of cooperativity between these sites.