KINETICS OF MANGANESE RECONSTITUTION AND THIOL-GROUP EXPOSITION IN DIALYZED RAT MAMMARY-GLAND ARGINASE

1. Rat mammary gland arginase is a metallo-enzyme dependent on Mn2+, which can be only partially substituted by Cd2+. 2. Reconstitution of the activity of dialyzed arginase by manganese is a two-phase process; the second phase is independent of the cation concentration, with a half-time recovery (t1/2) of 10.77 min. 3. The apparent K-m for Mn2+ is 280 mu M and 10.5 mu M for enzyme dialyzed for 24 and 72 hr, respectively. 4. Treatment with 5mM EDTA at pH6 totally inhibits enzyme activity, which is reconstituted by Mn2+. 5. Results obtained with iodocetamide treatment suggest the existence of sulphydryl groups accessible only when the enzyme is dialyzed.