Coenzyme Interactions

Abstract

Abstract Addition of Ni2+ to solutions of thiamine pyrophosphate causes shifting and broadening of the proton magnetic resonance signals of the thiamine moiety. The effect of variations of pH and temperature on these changes has been studied. The results indicate an interaction of the metal ion with both the pyrophosphate group and the N-1' atom of the pyrimidine ring. The shift-to-broadening ratio of the signal of the pyrimidine C-6' hydrogen, the ratio of broadening of the signals of the C-2' methyl group and the C-6' hydrogen, and examination of models all suggests that, as in Ni2+-ATP, the ring nitrogen is not a first sphere ligand of the metal ion, but that the interaction probably occurs by a hydrogen bond involving a molecule of water in the first coordination sphere. Unlike the ATP case, with thiamine pyrophosphate there is a strong temperature dependence of the broadening of the C-6' hydrogen signal; this suggests that there is an equilibrium involving folded and forms, with the unfolded structure predominating.