INTERACTIONS AND EFFECTS OF 2-HYDROXY-5-NITROBENZYL BROMIDE ON THE BOVINE HEART MITOCHONDRIAL F(1)-ATPASE

1. The F1-ATPase from bovine heart mitochondria was shown to chemicall y react and to absorb 2-hydroxy-5-nitrobenzyl bromide (HNB) with chang es in catalytic properties. 2. The treatment of the enzyme with HNB at concentrations below 0.5 mM resulted in an increase of V(m) and in an unchanged K(m). Above 0.5mM HNB elicited a concentration-dependent in hibition of F1. 3. HNB was found tightly bound to the enzyme epsilon-s ubunit whose tryptophan residue resulted modified. 4. The F1 activatio n appears the consequence of the covalent binding of the reagent to th e enzyme, whilst inhibition results from non-covalent, reversible bind ing. 5. The possibility that the epsilon-subunit of mitochondrial F1-A TPase may influence the functional or regulating domain of the enzyme is discussed.