Enzymatic Synthesis of a Blood Group B-related Pentaglycosylceramide by an α-Galactosyltransferase from Rabbit Bone Marrow

Abstract

Abstract An α-galactosyltransferase that catalyzes the biosynthesis in vitro of blood group B-specific pentaglycosylceramide from UDP-[14C]galactose and O-β-galactosyl (1→3)-O-β-(N-acetyl) glucosaminosyl (1←3)-O-β-galactosyl (1→4)-O-β-glucosyl (1 →1) ceramide was detected in homogenates of adult rabbit bone marrow. The enzyme was present in the supernatant solution obtained after homogenization of rabbit bone marrow in the presence of 0.6% Triton X-100 and centrifugation at 100,000 x g. The enzyme was precipitated from the supernatant solution at 0 to 45% saturation with ammonium sulfate. The 14C product of the reaction was isolated, purified, and analyzed for its constituents. It inhibited the hemagglutination reaction of human B-type cells and rabbit erythrocytes against human anti-B serum. The terminal [14C]galactose was cleaved 85% by the action of fig α-galactosidase. The Km values were 1.67 x 10-3 m and 1.43 x 10-4 m for the tetraglycosylceramide (LacTet-cer) and UDP-galactose, respectively.