Separation of beta-D-galactosidases in rabbit tissues: genetics of neutral beta-D-galactosidase

Three different types of beta-D-galactosidase (EC 3.2.1.23) could be distinguished in rabbit tissues using electrophoretic procedures. (1) Acid beta-D-galactosidase with a low mobility and maximal activity at pH 3-5 was found in the particulate fraction of various tissue homogenates. This enzyme hydrolyzed 4-methylumbelliferyl-D-galactoside, but no activity against other glycoside substrates could be demonstrated. The enzyme was inhibited by galactono-(1 leads to 4)-lactone. (2) Lactose-hydrolyzing beta-D-galactosidase with an intermediate mobility was found only in juvenile small intestine. Most of the activity was found in the particulate fraction of the cell. The enzyme hydrolyzed several other synthetic glycoside substrates besides lactose. It was most active at pH 5-6 and strongly inhibited by glucono-(1 leads to 5)-lactone but not much affected by galactono-(1 leads to 4)-lactone. (3) Neutral beta-D-galactosidase with a fast mobility and maximal activity at pH 6-8 was found in the soluble fraction of homogenates from liver, kidney, and small intestine. This enzyme also showed a broad substrate specificity; it possessed activity against aryl-beta-D-glucoside, -fucoside, and -galactoside substrates but not against lactose. The enzyme was strongly inhibited by glucono-(1 leads to 5)-lactone and (less) by galactone-(1 leads to 4)-lactone. Neutral beta-D-galactosidase and neutral beta-D-glucosidase (EC 3.2.1.21) are probably identical enzymes in the rabbit. Individual variation, in both electrophoretic mobility and activity, was found for neutral beta-D-galactosidase. Genetic analysis of the electrophoretic variants revealed that two alleles at an autosomal locus are responsible for this variation.