EXPOSURE TO GALACTOSE-OXIDASE OF GM1 GANGLIOSIDE MOLECULAR-SPECIES EMBEDDED INTO PHOSPHOLIPID-VESICLES

The exposure of GM 1 molecular species present in the native gangliosi de, carrying C18:1 or C20:1 long-chain bases (LCB), to Dactylium denro ides galactose oxidase was studied. When native GM1 (49.3% C18:1 and 5 0.7% C20:1 LCB, respectively), was inserted in dipalmitoylphosphatidyl choline vesicles and partially oxidized (10%), the proportion of C18:1 and C20:1 species in the oxidized GM1 was 59.6% and 40.4%, respective ly, suggesting a preferential action of the enzyme on the shorter spec ies. The V-max of the enzyme was higher on C18:1 GM1 than on C20:1 GM1 . The molecular species were affected without any preference after par tial (10%) oxidation of GM1 incorporated in egg phosphatidylcholine ve sicles or in micellar form. These data indicate that the exposure of t he terminal galactose moiety of GM1 ganglioside to galactose oxidase i s affected by the ganglioside ceramide composition as well as the phos pholipid environment, that presumably determine the distribution (mole cular dispersion, segregation) of the ganglioside within the membrane.