Dec 16, 1975

Subunit interactions in yeast glyceraldehyde-3-phosphate dehydrogenase

Biochemistry
S C MockrinD E Koshland

Abstract

The spontaneous inactivation of yeast glyceraldehyde-3-phosphate dehydrogenase was found to fit a simple two-state model at pH 8.5 and 25 degrees. The first step is a relatively rapid dissociation of the tetramer to dimers with the equilibrium largely in favor of the tetramer. In the absence of NAD+ the dimer inactivates irreversibly. The apoenzyme is quite stable with a half-life for complete activity loss proportional to the square root of the enzyme concentration. Perturbances of the protein structure (by pH, ionic strength, and specific salts), which have no effect on the tetrameric state of the molecule, result in an alteration of the cooperativity of NAD+ binding, the reactivity of the active-site sulfhydryl group, and the catalytic activity of the enzyme. Covalent modification of two of the four active-site sulfhydryl groups has profound effects on the enzymic activity which are mediated by changes in the subunit interactions. Sedimentation analysis and hybridization studies indicate that the interaction between subunits remains strong after covalent modification. Under normal physiological and equilibrium dialysis conditions the protein is a tetramer. Equilibrium dialysis studies of NAD+ binding to the enzyme at pH 8.5 ...Continue Reading

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Mentioned in this Paper

Macromolecular Compounds
Covalent Interaction
Apoenzymes
Nucleic Acid Hybridization Procedure
GAPDH gene
NAD+ Binding
NADH
Sulfhydryl Compounds
Plasma Protein Binding Capacity
Enzyme Activity

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