Enzymatic Hydrolysis of Sphingolipids. VI. Hydrolysis of Ceramide Glycosides by Calf Brain β-N-Acetylhexosaminidase

Trihexosylceramide (GalNAc-β-1,4-Gal-β-1,4-Glc-β-1,1-(2-N-acyl)sphingosine) was prepared and used as substrate for calf brain β-N-acetylhexosamini-dase. Two other glycosphingolipids, “globoside” from human erythrocyte stroma and the ganglioside which accumulates in brain tissue of patients with Tay-Sachs’ disease, were also hydrolyzed. The rate of hydrolysis of the latter compound was much slower than those of the other two substrates. The β-N-acetylglucosaminidase and β-N-acetylgalactosaminidase from calf brain did not hydrolyze these glycosphingolipids. The hydrolysis of trihexosylceramide had a pH optimum of 3.8, a K_m of 0.6 mM, and a V_max of 0.5 /umole/mg of protein per hr. It was inhibited by several lipids, by two “SH inhibitors,” by free and acetylated hexosamines, and by mono- or divalent ions. The hydrolysis of globoside was similar to that of trihexosylceramide in most respects. “Tay Sachs’ ganglioside” strongly inhibited the hydrolysis of trihexosylceramide. The possibility that this might be a cause for the accumulation of the latter compound in brain tissue of patients with Tay-Sachs’ disease is discussed.