Purification and Properties of Rat Small Intestinal Arginase

Abstract

Arginase [L-arginine amidinohydrolase EC 3.5.3.1] from rat small intestine was purified about 2, 200-fold and its properties were compared with those of the rat liver and kidney enzymes. Intestinal arginase was extremely labile on storage either at -10° or 4° and lost activity during purification unless 25mM L-valine was present.
The purified enzyme appeared to be homogeneous by disc electrophoresis and its molecular weight was estimated to be 120, 000 by Sephadex G-100 filtration. The enzyme was highly specific for L-arginine and showed maximal activity at pH 10.0 in the presence of Mn²⁺. The K_m for L-arginine was 19mM and the activity was competitively inhibited by L-lysine, L-ornithine, L-valine, L-isoleucine, L-leucine, and L-proline, and non-competitively by L-tryptophan.
The enzyme was almost completely inactivated by treatment with EDTA at pH 4.5, then immediately returning it to pH 7.4, and assaying in the absence of Mn²⁺, but some activity was detected when it was assayed in the presence of Mn²⁺. Similar phenomena were observed with rat liver and kidney arginase, but the latter two enzymes dissociated into subunits on EDTA treatment at low pH, while intestinal arginase did not.