On the structure of the diphosphopyridine nucleotide-cyanide complex.

Meyerhof, Ohlmeyer, and Mohle (1) reported that DPNl reacted with cyanide or bisulfite to form complexes having absorption spectra resembling that of DPNH. Colowick et al. (2) studied the cyanide reaction in more detail and showed that the ability to form a complex with cyanide is a general property of N1-substituted nicotinamide compounds. Because of the instability of the complex, these investigators made no attempt to isolate it. It has heretofore been assumed that addition of cyanide to DPN occurs at one of the a! positions, namely carbons 2 or 6, on the basis of the indirect evidence of Karrer et al. (3) that reduction of DPN occurred at one of these sites. In the light of the finding of Pullman et al. (4) that reduction of DPN occurs at the 4 or y position of the nicotinamide moiety, it was of interest to ascertain the site of addition of cyanide to DPN. In the present paper, data are presented which are consistent with the view that addition of cyanide occurs at the y position of the nicotinamide moiety rather than at either of the LY positions. This conclusion is based on the finding that the DPN-CN complex in heavy water undergoes deuterium exchange at the y position exclusively.