Mechanism of glycogen synthetase as determined by deuterium isotope effect and positional isotope exchange experiments

Journal Article · Mon Jul 25 04:00:00 EDT 1988 · J. Biol. Chem.; (United States)

OSTI ID:6902614

Kim, S C; Singh, A N; Raushel, F M

The reaction mechanism for glycogen synthetase from rabbit muscle was examined by alpha-secondary deuterium isotope effects and positional exchange experiments. Incubation of glycogen synthetase with (beta-/sup 18/O/sub 2/,alpha beta-/sup 18/O)UDP-Glc did not result in any detectable positional isotope exchange from the beta-nonbridge position to the anomeric oxygen of the glucose moiety. Glucono-1,5-lactone was found to be a noncompetitive inhibitor versus UDP-Glc. The kinetic constants, K(is) and K(ii), were found to be 91 +/- 4 microM and 0.70 +/- 0.09 mM, respectively. Deoxynojirimycin was a nonlinear inhibitor at pH 7.5. The alpha-secondary deuterium isotope effects were measured with (1-/sup 2/H)UDP-Glc by the direct comparison method. The isotope effects on Vmax and Vmax/K were found to be 1.23 +/- 0.04 and 1.09 +/- 0.06, respectively. The inhibitory effects by glucono-lactone and deoxynojirimycon plus the large alpha-secondary isotope effect on Vmax have been interpreted to show that an oxocarbonium ion is an intermediate in this reaction mechanism. The lack of a detectable positional isotope exchange reaction in the absence of glycogen suggests the formation of a rigid tight ion pair between UDP and the oxocarbonium ion intermediate.

• Research Organization: Texas A and M Univ., College Station (USA)
• OSTI ID: 6902614
• Journal Information: J. Biol. Chem.; (United States), Journal Name: J. Biol. Chem.; (United States) Vol. 263:21; ISSN JBCHA
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ANIMALS
BIOCHEMICAL REACTION KINETICS
DEUTERIUM
ENZYME INHIBITORS
ENZYMES
EVEN-EVEN NUCLEI
HYDROGEN ISOTOPES
ISOTOPE APPLICATIONS
ISOTOPE DILUTION
ISOTOPE EFFECTS
ISOTOPES
ISOTOPIC EXCHANGE
KINETICS
LIGASES
LIGHT NUCLEI
MAMMALS
MUSCLES
NUCLEI
ODD-ODD NUCLEI
OXYGEN 18
OXYGEN ISOTOPES
RABBITS
REACTION KINETICS
STABLE ISOTOPES
TRACER TECHNIQUES
VERTEBRATES