Model studies for isocitrate dehydrogenase: Interaction between Co(II) and isocitric acid

Abstract

Using potentiometry and visible absorption spectrophotometry it is shown that at pH 6 a complex is formed with 1:2 Co(II):isocitrate ratio, the cobalt atom being in a distorted octahedral environment. For the racemic compound all the carboxyl groups are symmetrical and the less acidic, that of CH 2COOH, is bound to cobalt. The electronic spectra of the racemic and chiral compounds are slightly different, showing a stereoselective effect. For the chiral compound the Δ ε 525 value is 0·21 ± 0·01. At higher pH, potentiometry shows the existence of two different complexes with a deprotonated hydroxyl group: at high cobalt and isocitrate concentrations a pink complex predominates with a cobalt atom in a distorted octahedral environment whereas at low concentration a blue complex is present with a cobalt atom in a trigonal bipyramidal environment.