Serotonine-nucleotide interaction studied by PMR. Explanation of the variability in association constants obtained from chemical shifts of different protons.

A study of the association of serotonine with 5'-AMP by PMR spectroscopy is described. The association constants obtained from the chemical shift of non-equivalent protons show considerable variation outside experimental error, a fact which wTas reported by several authors. To support the suppositon that small amounts of complexes of different stoichiometry, — which in general can hardly be detected —, are responsible for this phenomenon, computer simulation of various hypo­ thetical systems were investigated. The results clearly demonstrate that the neglect of minor fractions of complexes of different stoichiometries lead to significant variation in the association constants calculated for different protons, provided that these protons experience different magnetic enviroments in the different complexes.