An investigation of the nature of NADHX enzymatically produced from the abortive reaction of yeast glyceraldehyde phosphate dehydrogenase on NADH (in the absence of substrate) is in progress. Particular attention is given to the possible regulatory role this abortive reaction may have in the inhibition on activation of pyridine nucleotide dehydrogenases. The conditions for formation and decomposition of NADHX are compared with the conditions for formation and decomposition of NADHOH, the chemically hydrated NADH. A comparison between the biological activity of NADHOH and NADHX is made. In progress is an investigation of the reactivity scale for nucleophilic reactions of NAD and its analogues, and a comparison of this scale to similar scales. The structural effects on NADH hydration has been examined in some detail. The investigation of the effect of borate on nucleophilic reactions of pyridine nucleotides in enzymatic and nonenzymatic reactions is in progress.