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JBC, Vol. 252, Issue 7, 2346-2355, Apr, 1977
M. Schwyzer and R. L. Hill
Porcine A blood group-specific N-acetylgalactosaminyl-transferase required
either Mn2+, Cd2+, or Zn2+ for activity and 2'-O-alpha-fucosylgalactosides
as acceptor substrates. The presence of detergent stabilizes the enzyme but
is not essential for catalysis. To obtain information about the kinetic
mechanism of the transferase reaction, initial rate parameters have been
determined using 2'-fucosyllactose or A--mucin as acceptors, and Mn2+ or
Cd2+ as cosubstrates. 2'-Fucosyllactose is a competitive inhibitor with
respect to A--mucin and a noncompetitive inhibitor with respect to
UDP-N-acetylgalactosamine. UDP inhibits noncompetively with respect to
acceptor; thus UDP-N-acetylgalactosamine or acceptor can bind to the
transferase via an equilibrium random pathway. The transferase converts
human O blood type erythrocytes of A blood types. After exhaustive
glycosylation, 3 X 10(6) N-acetylgalactosaminyl residues were incorporated
per cell. Gel electrophoretic analysis of the labeled erythrocyte membranes
indicates that glycoproteins with apparents molecular weights from 30,000
to 100,000 have been glycosylated; glycolipids account for only 15% of the
labeled material, although pure H-glycolipid is a good acceptor. The
transferase, with its strict acceptor specificity, can thus be used as a
tool to study the biosynthesis and function of glycolipids and
glycoproteins.
Porcine A blood group-specific N-acetylgalactosaminyltransferase
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