ACID MUCOPOLYSACCHARIDES AS DISPERSING AGENTS IN LYSOSOMAL DIGESTION

Abstract

Mucopolysaccharides are known to coat cell surfaces. They can thereby reach secondary lysosomes when the cell membrane invaginates to form pinocytic vacuoles.In the mucopolysaccharidoses, lysosomes accumulate enormous quantities of mucopolysaccharides. We propose that this is an exaggeration of a normal process, during which hydrolase activities are generally increased while a few are decreased. One of the intriguing problems of lysosomal physiology is the way in which water-insoluble substances such as lipids are digested. To accomplish this in vitro, detergents are needed. Some micellar system is most likely involved, as suggested by the occasional occurrence of myelin bodies even in normal lysosomes. We have compared sphingomyelinase activity using either Triton-X 100 and chondroitin sulfate or hyaluronic acid. Using a large concentration of mucopolysaccharide (up to 4 mg per ml of incubation mixture), activities close to those obtained with the detergent were observed. Since glycolipids accumulate in mucopolysaccharidoses, it would seem that either dermatan sulfate is not a suitable dispersing agent, or that it combines with the enzyme as suggested by the alterations in electrophoretic mobility which were reported by Kint et al, (Science:181, 352, 1973). (Supported in part by PHS Grant HD-04612.)