Isoenzymes of rabbit liver β-galactosidase

Effects of several alcohols on glycosidase activities in rat liver and brain

1. beta-D-Galactosidase, beta-D-glucuronidase and beta-NAc-D-glucosaminidase spec. acts from liver displayed statistically significant differences after treatments with certain alcohols. 2. No statistically significant difference was found for the kinetic parameters (Km and Vmax) of the indicated glycosidase activities. 3. beta-D-Glucuronidase and beta-NAc-D-glucosaminidase spec. acts from brain tissue showed statistically significant differences after treatments with certain alcohols. 4. beta-D-Glucuronidase and beta-NAc-D-glucosaminidase activities from liver showed a statistically significant decrease in the presence of in vitro ethanol. Tolerance effects were not observed.

Comparative studies of two acid beta-galactosidases from rabbit and bovine kidney

Comparative studies of two acid beta-galactosidases from rabbit and bovine kidney have been made. The enzyme from rabbit (enzyme I) was purified 450-fold, and the activity of the bovine enzyme (enzyme II) was enriched 250-fold using conventional purification methods. Both purified enzymes were characterized and their properties were compared. Enzyme I showed a lower optimal temperature and was less pH stable. Enzyme II appeared to be homogeneous in charge, in contrast to the heterogeneity observed for enzyme I. Studies on their specificity using natural substrates showed that enzyme I hydrolyzed GM1, asialofetuin and lactose. However, enzyme II was only able to cleave galactose from the disaccharide. Some of the carbohydrates tested acted as activators for enzyme II, suggesting a mechanism of transglycosilation. Using lactose as substrate we confirmed the ability of enzyme II to transfer galactose residues to D-maltose and N-acetylgalactosamine.

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.