Reactions of d-glyceraldehyde 3-phosphate dehydrogenase facilitated by oxidized nicotinamide–adenine dinucleotide

摘要

Transient kinetic methods have been used to study the influence of NAD⁺ on the rate of elementary processes of the reversible oxidative phosphorylation of d-glyceraldehyde 3-phosphate catalysed by d-glyceraldehyde 3-phosphate dehydrogenase. In the pH range 5–8 NAD⁺ is bound to the enzyme during the following elementary processes of the mechanism: phosphorolysis of the acyl-enzyme, its formation from 1,3-diphosphoglycerate and the enzyme and the formation and breakdown of the glyceraldehyde 3-phosphate–enzyme complex. The rates of these four elementary processes only equal or exceed the turnover rate of the enzyme when NAD⁺ is bound and are as much as 10⁴ times the rates in the absence of NAD⁺. Autocatalysis of the reductive dephosphorylation of 1,3-diphosphoglycerate occurs when glyceraldehyde 3-phosphate release is rate determining because NAD⁺ is a reaction product. An important feature of the enzyme mechanism is that the negative-free-energy change of a chemical reaction, acyl-enzyme formation, is linked in a simple way to the positive-free-energy change of a dissociation reaction, NAD⁺ release.