Binding of an acceptor substrate analog enhances the enzymatic activity of human blood group B galactosyltransferase.
The hydrolysis of the donor substrate uridine diphosphate galactose (UDP-Gal) by human blood group B galactosyltransferase (GTB) has been followed by nuclear magnetic resonance in the presence and in the absence of an acceptor substrate analog. It is observed that the presence of the acceptor substrate analog promotes hydrolysis of UDP-Gal. Subsequent analysis of the kinetics of the enzymatic hydrolysis suggests that this effect is due to an increased affinity of GTB for UDP-Gal in the presence of the acceptor analog. Isothermal titration calorimetry experiments substantiate this conclusion. As hydrolysis may be understood as a glycosyl transfer reaction where water serves as universal acceptor, we suggest that in general the binding of acceptor substrates to retaining glycosyltransferases modulates the rate of glycosyl transfer. In fact, this may point to a general mechanism used by retaining glycosyltransferases to discriminate acceptor substrates under physiological conditions.
Sindhuwinata
Nora
N
Institute of Chemistry, University of Luebeck, Ratzeburger Allee 160, 23538 Luebeck Germany.
Munoz
Eva
E
Munoz
Francisco Javier
FJ
Palcic
Monica M
MM
Peters
Hannelore
H
Peters
Thomas
T
D001665:Binding Sites; D002151:Calorimetry; D004789:Enzyme Activation; D005700:Galactosyltransferases / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D013379:Substrate Specificity; D014531:Uridine Diphosphate Galactose / Q000378:metabolism*; D014867:Water / Q000378:metabolism
D014867:Water; D014531:Uridine Diphosphate Galactose; D005700:Galactosyltransferases; C023155:blood-group-substance alpha-D-galactosyltransferase