Comparative biochemistry of a cytosolic artiodactyl glycosidase

Artiodactyls possess abundant neutral glycosidase activity in liver, kidney and intestine. This enzyme is cytosolic and displays a more neutral pH optimum, more acidic isoelectric point and broader substrate range than the corresponding acidic beta-galactosidases. The neutral glycosidases were more thermolabile than the respective acidic beta-galactosidases and displayed a relative molecular mass approximating 60 kDa. This isozyme appeared to be a minor species in both rat and dog liver. The porcine enzyme was studied in more detail. Porcine neutral glycosidase activity was detected in 45-day gestational fetuses in both liver and kidney but not brain. Fetal kidney activities were about half those observed in adult kidney extracts. Porcine neutral glycosidase was immunologically distinct from acidic beta-galactosidase and was immunologically similar to the corresponding isozymes from deer, ovine and bovine liver. Porcine neutral glycosidase was moderately inhibited by D-galactonic acid gamma-lactone and strongly inhibited by D-gluconic acid delta-lactone; however, acidic beta-galactosidase was not inhibited by the delta-lactone. Inhibition by the gamma-lactone was competitive for both enzymes. 4-Methylumbelliferyl-beta-D-galactoside,-glucoside and -xyloside competed for the same active site. A polymorphism for fast- and slow-migrating isozymes of porcine neutral glycosidase was observed, which appeared to be under genetic control.