Conformational changes in glutamine synthetase from Escherichia coli. I. Binding of manganese ion in relation to some aspects of the enzyme structure and activity

The Story of Glutamine Synthetase Regulation

“…Subsequently, Mark Fisher demonstrated that in the presence of ATP the dissociated subunits could also be converted to the "taut" form by the E. coli chaperonin (12). In continuing studies, Shapiro and Ginsburg demonstrated that GS has two binding sites for divalent cations; one is involved in the interconversion of the "relaxed" and "tightened" configurations, whereas the other is involved in the binding of the ATP substrate to the enzyme (13,14). Subsequently, Shapiro took a sample of the pure enzyme to the National Institute for Medical Research in London, where R. C. Valentine, an expert in electron microscopy, examined its structure.…”

Regulation of Escherichia coli Glutamine Synthetase

“…Metal-ion-binding study monitored by equilibrium dialysis with 54Mn(II) revealed the existence of three classes of divalent-cationbinding sites as judged by affinity differences (55). Saturation of the high-affhity site, nl, in each subunit with Mg(II), Mn(II), Ca(II), or Co(I1) is correlated to converting the relaxed enzyme to its active form (2,52,56-59).…”

“…Metalion-dependent activity study shows that saturation of the nl and n2 sites by Mn(I1) ions is absolutely required for expressing Mn(I1)-dependent enzymic activity (58). Evidence in support of Mg(I1) binding to the same nl site as Mn(I1) includes the following: (a) Equilibrium dialysis data show that Mg(I1) competes with Mn(I1) at the high-affinity nl site (55). (b) Both cations induce the same ultraviolet spectral change when added to the relaxed enzyme.…”

Trace cobalt speciation in bacteria and at enzymic active sites using emission Mössbauer spectroscopy

“…Bacterial GSs are dodecameric proteins; the GS molecule is formed from two face-to-face hexameric rings of total 12 subunits with 12 active sites between the monomers, each having two divalent cation-binding sites, n1 and n2, which differ in their affinity for divalent cations [31]. For all GSs, including that of A. brasilense, divalent cations (commonly, Mg 2+ , Mn 2+ or Co 2+ ) are necessary for the activity to be expressed [9,20,30,31,32]. Along with the twelve n1 sites and twelve n2 sites, GS from E. coli has 48 additional metal-binding sites per oligomer with relatively lower affinity [32].…”