ISOLATION OF 2 FORMS OF AN ACTIVATOR PROTEIN FOR THE ENZYMIC SPHINGOMYELIN DEGRADATION FROM HUMAN GAUCHER SPLEEN

Two activator proteins for sphingomyelin degradation were isolated from heat-treated extracts of human Gaucher spleen. The separation was based on the degree of affinity of the activators for Con A [concanavalin A]-Sepharose. Activator A1, which had affinity for Con A-Sepharose, was purified 1430-fold and activator A2, which had no affinity for Con A-Sepharose, 2140-fold as compared with the original heat-treated extracts. The molecular masses of activator A1 and activator A2 were 6000 and 3500 Da [dalton], respectively, as determined by dodecyl sulfate electrophoresis, and .apprx. 5000 Da as measured in the presence of 8 M urea. The 2 activators had similar properties, and a similar but not identical amino-acid composition. Both were shown to form a complex with sphingomyelin and stimulate the degradation of sphinogomyelin by normal fibroblast homogenates, and by an .apprx. 1430-fold purified sphingomyelin phosphodiesterase (acid spingomyelinase) from normal human urine. This stimulation was greatly reduced after incubation with pronase E. The enzymic degradation of glucosylceramide and galactosylceramide was not affected by these activators.