Complex of D-glyceraldehyde-3-phosphate dehydrogenase with Cu2+ ion. I. The apoenzyme-Cu complex.
D-Glyceraldehyde-3-phosphate dehydrogenase binds one Cu2+ ion per subunit, which results in the formation of a specific metal-protein complex. This complex exhibits a sharp absorption band around 370 nm, and a broad, small absorption band in the 600-700 nm region. The shape of the absorption spectrum of Cu-GAPD complex in the visible range depends on the anionic composition of the solution. The Cu-GAPD complex is stable in solutions containing phosphate or pyrophosphate anions, but undergoes a slow change in sulfate-, and a rapid change in chloride-containing solutions. The Cys-149 residue of the enzyme is essential for the formation of the Cu-GAPD complex. The sharp absorption at 370 nm presumably corresponds to a charge transfer interaction between the sulfur and the metal ion. Similar absorption bands are shown by the Cu-complexes of papain and thiol-alcalase enzymes. It is assumed that in addition to the reactive thiol groups an imidazole residue in the active site of these enzymes is also involved in the complex formation, and the specific Cu-GAPD Cu-papain and Cu-thiol-alcalase complexes contain a Cys-Cu-His chelate structure.