SELF-ASSOCIATION OF NICOTINAMIDE ADENINE DINUCLEOTIDES IN AQUEOUS-SOLUTION

The self-association of the nicotinamide adenine dinucleotides NAD and NADH was studied in aqueous solution by means of ultraviolet spectroscopy. Measurements were made of the hypochromic effects of these compounds as a function of concentration over the range 10(-6) 10(-1) M. The effects were interpreted in terms of the processes of dimerization and polymerization. The corresponding self-association constants were calculated. Both processes are evidenced for NAD by the band at 259.0 nm, whilst for NADH the two processes are evidenced separately by two bands at 259.0 and 3 38.0 nm, which also show different behaviour with temperature. A complementary study of the self-association of nicotinamide as a function of pH was carried out in order to interpret the results of the analysis for NAD and NADH; our previous results on the self-association of adenine derivatives were also used. The differences observed between NAD and NADH are discussed in detail with relation to the interaction of their constituent units. The results of this work show that the self-association processes of NAD and NADH could be significant in determining the mode of interaction of these coenzymes in experiments of binding to corresponding enzymes.