We have obtained direct evidence that the majority of the sirohydrochlorin chromophore in the dissimilatory sulfite reductase desulfoviridin from Desulfovibrio gigas, is not associated with any metal. The evidence comes from resonance Raman measurements of native and deuterated samples of desulfoviridin. The breathing mode v4 (or v*4) at 1336 cm-1 in the native enzyme is downshifted to 1326 cm-1 upon deuteration. This mode is not sensitive to deuteration if a metal is present at the center of the chromophore inside protein or in solution. The results also establish the existence of exchangeable core hydrogen(s) at the pyrrolic nitrogen(s).
- Raman spectroscopy
- Sulfite reductase