The Mechanism of Inactivation of Glyceraldehyde 3-Phosphate Dehydrogenase by Tetrathionate, o-Iodosobenzoate, and Iodine Monochloride

The reversible and irreversible inactivation of pig muscle glyceraldehyde 3-phosphate dehydrogenase (d-glyceraldehyde-3-phosphate:nicotinamide adenine dinucleotide oxidoreductase (phosphorylating), EC 1.2.1.12) with tetrathionate, o-iodosobenzoate, and iodine monochloride has been studied. This investigation has revealed that tetrathionate reacts stoichiometrically with the catalytically active sulfhydryl group of the enzyme to form a sulfenyl thiosulfate derivative under reversible conditions. The sulfenyl thiosulfate derivative of the enzyme is stable at 0°, but decomposes at higher temperatures. During this decomposition the enzyme is irreversibly inactivated. The experimental evidence presented strongly indicates that the catalytically active sulfhydryl group is converted to a stabilized sulfenic acid during its stoichiometric reaction with o-iodosobenzoate at 0°. The reaction of iodine monochloride is complex. However, at 0° it reacts with the catalytically active sulfhydryl group of the enzyme. The product of this reaction is in part a sulfenyl iodide derivative and in part what again appears to be a sulfenic acid derivative of this essential sulfhydryl group. At 26° iodine monochloride irreversibly inactivates the enzyme. During this irreversible inactivation, iodine is not substituted into tyrosine or histidine.