Purification and Characterization of an Activator Protein for the Degradation of Glycolipids GM2and GA2by Hexosaminidase A

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Abstract
The activator protein for the degradation of glycolipids GM2 and GA2 by hexosaminidase A was purified some 2500-fold from normal human kidney. It has a MW of .apprx. 25,000, is heat-stable up to 60.degree. C, possesses an isoelectric point of pH 4.8 and is digestible by proteases. Enzymic degradation of the lipid substrates in the presence of this activator proceeds optimally at pH 4.2. The mode of action of the activator was also studied: the protein most probably complexes lipid molecules and presents them to the enzyme which otherwise cannot attack the aggregates formed by the lipids in aqueous solution. The hydrolysis of water-soluble synthetic substrates is not affected by the activator protein. The activator is highly specific for hexosaminidase A: hydrolysis of glycolipids GA2 and GM2 by the hexosaminidase B isoenzyme is almost not enhanced by this protein. The isoenzymes'' lipid substrate specificity measured in the presence of the activator is entirely different from that obtained with detergents, and can satisfactory account for the lipid storage pattern observed in patients with variant forms of infantile GM2-gangliosidosis.

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