Purification and properties of a heat-stable glucocerebrosidase activating factor from control and Gaucher spleen

Abstract

Gaucher's disease is a lysosomal storage disease caused by a deficiency in the enzyme glucocerebrosidase. A small, heat-stable glycoprotein first obtained from Gaucher spleen (Ho, M. W., and O'Brien, J. S. (1971) Proc. Natl. Acad. Sci. U. S.A. 68, 2810-2813) has been observed to stimulate the activity of glucocerebrosidase isolated from normal tissue. It has been suggested that this material might be important in the physiological catabolism of glucocerebroside in normal individuals (Ho, M. W. (1974) in Enzyme Therapy in Lysosomal Storage Diseases (Tager, J. M., Hooghwinkel, G. J. M., and Daems, W. Th., eds) pp.239-246, North-Holland Publishing Co., Amsterdam). In order to investigate this suggestion, glucocerebrosidase activating factors were isolated and purified from control and Gaucher spleen and characterized. Although approximately the same mass of activator was isolated from both spleens, the two activators differ from one another in a number of important respects: (a) the activator from the control spleen is only 6 per cent as active (on a protein basis) as the activator from Gaucher spleen; (b) the amino acid compositions of the purified activators are significantly different; and (c) carbohydrate analysis of the purified activators indicates that the activator from Gaucher spleen is a glycoprotein, while that from control spleen is not. Comparative kinetic studies demonstrate that the anionic detergent, sodium taurocholate, and the acidic phospholipid, phosphatidylinositol, both stimulate glucocerebrosidase activity to a larger extent than the activator substance from Gaucher spleen. The activator from Gaucher spleen and human liver glucocerebrosidase both appear to contain significant hydrophobic character. We conclude that the activator is probably not physiologically important in the catabolism of glucocerebroside in normal tissues. The significance of the occurrence of this apparently unique glycoprotein activator in Gaucher spleen remains obscure; however, its presence represents another interesting aspect of Gaucher's disease that warrants further investigation.