Characterization of neutral isozymes of human alpha-glucosidase: differences in substrate specificity, molecular weight and electrophoretic mobility.

We have previously defined two isozymes of neutral alpha-glucosidase (alpha-D-glucoside glucohydrolase, EC 3.2.1.20) on the basis of differences in electrophoretic mobility and designated these neutral alpha-glucosidase AB and alpha-glucosidase C (Swallow, D.M., Corney, G., Harris, H. and Hirschhorn, R. (1975) Ann. Hum. Gen. 38, 391-406). We now describe differences between the two isozymes with respect to molecular weight, solubility in (NH4)2SO4, glycosylation, isoelectric point and substrate specificities. Neutral alpha-glucosidase C is precipitable in 40-60% (NH4)2SO4, has a molecular weight of 92 000, an isoelectric point of 5.5 and releases glucose from glycogen as well as from low molecular weight artificial and natural substrates containing alpha 1-4 glucosidic linkages. Neutral alpha-glucosidase AB precipitates at 0-40% (NH4)2SO4, binds to concanavalin A, has a molecular weight of greater than 150 000, and does not utilize alpha 1-4 linked glucose substrates larger than a disaccharide. Neutral alpha-glucosidase AB migrates more rapidly to the anode than alpha-glucosidase C when agarose, Cellogel, acrylamide or starch are used as support media. Both isozymes are equally inhibited by Zn2+.