Interactions and effects of 2-hydroxy-5-nitrobenzyl bromide on the bovine heart mitochondrial F1-ATPase.

1. The F1-ATPase from bovine heart mitochondria was shown to chemically react and to absorb 2-hydroxy-5-nitrobenzyl bromide (HNB) with changes in catalytic properties. 2. The treatment of the enzyme with HNB at concentrations below 0.5 mM resulted in an increase of Vm and in an unchanged Km. Above 0.5 mM HNB elicited a concentration-dependent inhibition of F1. 3. HNB was found tightly bound to the enzyme epsilon-subunit whose tryptophan residue resulted modified. 4. The F1 activation appears the consequence of the covalent binding of the reagent to the enzyme, whilst inhibition results from non-covalent, reversible binding. 5. The possibility that the epsilon-subunit of mitochondrial F1-ATPase may influence the functional or regulating domain of the enzyme is discussed.