Role of metals in enzymatic reactions. Part 2.—Kinetics of complex formation in model systems involving manganese(II) and 8-hydroxyquinoline

Abstract

The temperature-jump relaxation method has been used to measure the kinetics of formation of the 1:1 complex between magnesium and 8-hydroxyquinoline (oxine), and the magnesium-uramil NN diacetate, -adenosine 5′ triphosphate and -polytriphosphate complexes have also been investigated. In all cases the data are consistent with a two-path mechanism involving the addition to the magnesium species of the oxine anion or the oxine molecule. The first ligand has comparatively little influence on the rate at which magnesium reacts with a second ligand, and the kinetics of complex formation appear to follow the pattern already found for 1:1 complexes. These systems may be regarded as models for the enzyme-metal-substrate complexes which have been postulated as intermediates in many metal-catalyzed enzyme reactions. The observed rate constants are discussed in the context of a kinetic model to explain the differing catalytic powers of various metals such as magnesium and calcium.