EPR and EXAFS studies of glucose isomerase activation by divalent metals |
| |
Authors: | S Branner G Marg R Ozer D S Clark |
| |
Institution: | (1) NOVO Industry A/S Novo Alle, DK-2880 Bagsvaerd, Denmark;(2) School of Chemical Engineering, Cornell University, 14853 Ithaca, New York, USA |
| |
Abstract: | The interactions of Mn2+ and Co2+ with glucose isomerases from three microbial sources have been studied using various direct physical methods. Co2+ was found to activate each enzyme, although the degree of activation varied significantly for enzymes from different organisms. EPR spectroscopy measurements revealed that dissimilarities in the coordination sphere of enzyme-bound Mn2+ accompanied the differences in enzyme activity. Variations in the EPR spectra of a nitroxide spin label coupled to two of the three isomerases, possibly near their active sites, were also observed. In no case was the EPR spectrum influenced by Co2+ addition, a result discordant with the hypothesis that Co2+ activates the enzyme by inducing a conformational change. The proximal biochemical environment of enzymebound Co2+ was also examined using EXAFS spectroscopy. This method showed that glucose causes notable changes in the ligand environment of the enzyme-bound metal, suggesting the formation of an enzyme-metal-substrate bridge complex. The significance of these results relative to possible reaction mechanisms is discussed. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|