FUNCTION OF SAPOSIN-C IN THE RECONSTITUTION OF GLUCOSYLCERAMIDASE BY PHOSPHATIDYLSERINE LIPOSOMES

The function of saposin C (Sap C), a glucosylceramidase activator prot ein, in the enzyme stimulation by phosphatidylserine (PS) liposomes ha s been investigated. Using gel filtration experiments evidence was obt ained for Sap C binding to PS large unilamellar vesicles (LUV) but not to glucosylceramidase. PS LUV which by themselves are unable to tight ly bind and stimulate the enzyme, acquire the capacity to also bind th e enzyme after interaction with Sap C, making it express its full acti vity. Our results indicate that the primary step in the Sap C mode of action resides in its association with PS membranes; in turn, this ass ociation promotes the interaction between the membranes and glucosylce ramidase.