Investigations on the Interaction of NADH with Cu(II): ESR and Optical Absorption Spectroscopy

Abstract

The interaction of the transition metal ion Cu(II) with NADH and its constituents has been investigated by means of electron spin resonance (ESR) and optical absorption spectroscopy. It has been shown by the decrease of the 340 nm absorption band of NADH that NADH is oxidized rapidly in the presence of Cu(II) ions. One Cu(II) ion seems to be responsible for more than one oxidation. In aquoeous solution, Cu(I) is reoxidized very rapidly to Cu(II). Thereafter, Cu(II) seems to form slowly a complex with NAD, as can be seen by the shift of the d-d band of the aquo complex from 800 nm to 690 nm. The molar extinktion coefficient increases concomitantly. This complex, then, seems to be stable for several weeks. The coordination sites of the NAD molecule seem to be N(7) of the adenine residue and 0 of the adjacent phosphate group. This can be concluded from the ESR and optical results obtained with Cu(II)-AMP complexes. Since both of these complexes exhibit very similar g-values and d-d-transition energies, it might be assumed, therefore, that Cu(II) is bound to the same ligand atoms. Consequently, Cu(II) ions migth induce changes in the steric configuration of NAD.