title: Octahedral metal coordination in the active site of glyoxalase I as evidenced by the properties of Co(II)-glyoxalase I.
abstract: Co(II)-glyoxalase I has been prepared by reactivation of apoenzyme from human erythrocytes with Co2+. The visible absorption spectrum showed maxima at 493 and 515 nm and shoulders at 465 and 615 nm. The absorption coefficients at 493 and 515 nm were 35 and 33 M-1 cm-1/cobalt ion, respectively; i.e. 70 and 66 M-1 cm-1 for the dimeric metalloprotein. The product of the enzymatic reaction, S-D-lactoylglutathione, although binding to Co(II)-glyoxalase I, had no demonstrable effect on the visible absorption spectrum, indicating binding outside the first coordination sphere of the metal. The EPR spectrum at 3.9 K was characterized by g1 approximately 6.6, g2 approximately 3.0, and g3 approximately 2.5, and eight hyperfine lines with A1 = 0.025 cm-1. Binding of the strong competitive inhibitor S-p-bromobenzylglutathione to Co(II)-glyoxalase I gave three g values: 6.3, 3.4, and 2.5, indicating a conformational change affecting the environment of the metal ion. Both optical and EPR spectra strongly suggest a high spin Co2+ with octahedral coordination in the active site of the enzyme. The similarities in kinetic properties between native Zn(II)-glyoxalase I and enzyme substituted with Mg2+, Mn2+, or Co2+ is consistent with the view that these enzyme forms have the same metal coordination in the protein.
mesh_terms: D001665:Binding Sites; D003035:Cobalt / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D006801:Humans; D007700:Kinetics; D007791:Lactoylglutathione Lyase / Q000378:metabolism*; D008190:Lyases / Q000378:metabolism*; D046911:Macromolecular Substances; D008345:Manganese / Q000378:metabolism; D013053:Spectrophotometry; D015032:Zinc / Q000378:metabolism
chemical_list: D046911:Macromolecular Substances; D003035:Cobalt; D008345:Manganese; D008190:Lyases; D007791:Lactoylglutathione Lyase; D015032:Zinc