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 j-phosphate dehydrogenase (n-glyceraldehyde-d-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.