Purification by affinity chromatography and characterization of a neutral alpha-glucosidase from horse kidney.

A horse kidney neutral alpha-D-glucosidase (alpha-D-glucoside glucohydrolase, EC 3.2.1.20) was purified about 580-fold with a yield of 33% by an affinity chromatography technique using the p-aminophenyl-beta-D-maltoside, a substrate derivative, as ligand. The purified enzyme, homogeneous in polyacrylamide gel electrophoresis, was a glycoprotein with a molecular weight of 280 000 as calculated by gel filtration and its isoelectric focusing points was found to be pH 4.1. The purified enzyme was able to hydrolyze various substrates having (alpha-1,2), (alpha-1,3), (alpha-1,4), and (alpha-1,6) glucosidic linkages. The V/Km ratio shows that the (alpha-1,4) linkages are the best substrates. The pKm of the purified enzyme determined at different pH values indicated that two ionizable groups with pK values 5.2 and 6.9 could be essential in the active site. Enzyme modification with cardodiimide abolished the maltase activity. The turanose, a substrate analogue, protected the enzyme against this inactivation.