Inhibition of dextransucrase by Zn 2+, Ni 2+, Co 2+, and Tris(hydroxymethyl)aminomethane (Tris)

Abstract

Initial rate kinetics of polysaccharide formation indicate that Zn 2+, Ni 2+, and Co 2+ inhibit dextransucrase [sucrose: 1,6-α- d-glucan 6-α- d-glucosyltransferase, EC 2.4.1.5] by binding to two types of metal ion sites. One type consists of a single site and has a low apparent affinity for Ca 2+. At the remaining site(s), Ca 2+ has a much higher apparent affinity than Zn 2+, Ni 2+, or Co 2+, and prevents inhibition by these metal ions. These findings are consistent with a two-site model previously proposed from studies with Ca 2+ and EDTA. Initial rate kinetics also show that Tris is competitive with sucrose, but that, unlike Zn 2+, Tris does not bind with significant affinity to a second site. This argues that there is a site which is both the sucrose binding site and a general cation site.