NAD+ analogue binding to glyceraldehyde-3-phosphate dehydrogenase.

A series of NAD+ analogues, modified on the pyridinium ring, have been tested for their enzymic properties in reactions with D-glyceraldehyde-3-phosphate dehydrogenase form sturgeon muscle, rabbit muscle and Bacillus stearothermophilus. The observed activity, inhibition and binding data are correlated to the structure of the enzyme and coenzyme analogue by model building on a Vector General interactive graphic display system using coordinates from the B. stearothermophilus holoenzyme structure. Most of the analogues with substituents in the pyridinium-3 position could be bound to glyceraldehyde-3-phosphate dehydrogenase, either in manner similar to NAD+ or in a completely different way with the substituted pyridinium ring rotated 110 degrees or more around the glycosidic bond. This indicates different possible modes of binding of NAD+ analogues within the pyridinium binding subsite. Analogues with substituents in the pyridinium-4 position are shown to be weakly bound to glyceraldehyde-3-phosphate dehydrogenase. This is explained by a strong interaction of the substituent in the 4 position with the residues Asn-313 and Cys-149.