Possible involvement of manganese in the catalytic mechanism of bovine liver arginase.

1. Bovine liver arginase followed Michaelis-Menten kinetics in the pH range of 4.5-9.0. The variation of vi with pH implied that a basic group (pKa 8.7) functions at the catalytic site. 2. Treatment of the enzyme with N-ethylmaleimide showed that there are no critical sulfhydryl groups on the enzyme. 3. The less selective reagent, 3-bromopyruvate, caused biphasic inactivation which was unaffected by the presence of ornithine. 4. The data pointed against critical involvement of active site amino acid side chains in the catalytic sequence in arginase. 5. The observed pH-rate profile may reflect ionization of metal-bound water.