Characteristics of beta-galactosidase in the mucosa of the small intestine of infant rats. Physicochemical properties.

1. The characteristics of acid and neutral beta-galactosidases isolated chromatographically from homogenates of the mucosa of the jejunum and ileum of suckling rats were studied. 2. The minimal molecular weight of the acid beta-galactosidase, as estimated by gel filtration on Sephadex G-200, was in the range 83000-105000, whereas for the neutral beta-galactosidase the estimated molecular weight was in the range 360000-510000. 3. The acid and neutral beta-galactosidases were inhibited competitively by galactono-(1-->4)-lactone, with respective K(i) values of 0.15mm and 1.1mm. Only the acid beta-galactosidase was inhibited competitively by sodium galactonate (K(i) 0.17mm). 4. Heat inactivation of both beta-galactosidases occurred according to first-order kinetics. The neutral enzyme was more labile, but bovine serum albumin protected acid enzyme only. 5. Urea treatment inactivated both beta-galactosidases, the neutral beta-galactosidase being more sensitive than the acid beta-galactosidase. 6. No differences were found between preparations from the jejunum and ileum.