The function of carbohydrate moiety and alteration of carbohydrate composition in human alkaline phosphatase isoenzymes.

The relationship between the structure and function of alkaline phosphatase (orthoposphoric monoester phosphohydrolase (alkaline optimum), EC 3.1.3.1) isoenzymes is under investigation in a number of laboratories. The present study deals with the effects of glycosidase digestion on the alkaline phosphatase isoenzymes. Changes in physicochemcial properties, activity, affinity for various lectins and blood group antisera, carbohydrate composition and biological half-life were investigated. The desialylated hepatic enzyme was shown to be more heat labile and more sensitive to protease digestion in the presence of 0.5% sodium dodecyl sulfate than native hepatic enzyme. Helix contents of the native and desialated hepatic enzyme were calculated to be 39.0 and 30.8%, respectively, and apparent molecular weights 175,000 and 167,000, respectively. Intestinal enzyme preparations treated with alpha-mannosidase, exo-N-acetyl-Dglucosaminidase and endo-N-acetyl-D-glucosaminidase-D displayed a decrease in enzyme activity. Among these, the alpha-mannosidase-treated enzyme activity was the most clearly reduction. The maximum activity of the alpha-mannosidase-treated intestinal enzyme was observed to change from 40 mM Mg2+ to 5--10 mM Mg2+.