| Abstract: | Glyceraldehyde 3-phosphate dehydrogenase (D-glyceraldehyde-3-phoshate:nicotinamide adenine dinucleotide oxidoreductase (phosphorylating), EC 1.2.1.12) forms a complex with 3-pyridinealdehyde-NAD which survives precipitation with 7% perchloric acid. The molar ratio bound 3-pyridinealdehyde-NAD to the enzyme is 2.5 to 2.9. Lactate, malate, and alcohol dehydrogenases do not form acid-precipitable complexes with 3-pyridinealdehyde-NAD. 3-Pyridinealdehyde-deamino-NAD or glyceraldehyde 3-phosphate also forms an acid-stable complex with glyceraldehyde 3-phosphate dehydrogenase; however, NAD, 3-acetylpyridine-NAD, or thionicotinamide-NAD does not produce an acid-stable complex. Incubation of the glyceraldehyde 3-phosphate dehydrogenase with glyceraldehyde 3-phosphate, acetyl phosphate, iodoacetic acid, or iodosobenzoate inhibits the formation of the acid-stable complex with 3-pyridinealdehyde-NAD. Glyceraldehyde 3-phosphate or 3-pyridinealdehyde-NAD also prevents carboxymethylation of the active site cysteine-149 by14-C]iodoacetic acid. These studies indicate that the aldehyde group of 3-pyridinealdehyde-NAD forms a thiohemiacetal linkage with cysteine-149 which is the substrate binding site for the dehydrogenase reaction. These findings may account for the fact that 3-pyridinealdehyde-NAD strongly inhibits the dehydrogenase and esterase activities of 3-pyridinealdehyde-NAD forms a thiohemiacetal linkage with cysteine-149 which is the substrate binding site for the dehydrogenase reaction. These findings may account for the fact that 3-pyridinealdehyde-NAD strongly inhibits the dehydrogenase and esterase activities of glyceraldehyde 3-phosphate dehydrogenase which require reduced cysteine-149. However, the analogue does not inhibit the acetyl phosphates activity of the enzyme for which the active site sulfhydryl residues must be oxidized. |
