EXOGENOUS LIGAND-BINDING TO PSEUDOMONAS-STUTZERI NITROUS-OXIDE REDUCTASE

The effects of azide, chloride, and nitric oxide on the copper sites i n Pseudomonas stutzeri nitrous oxide reductase have been examined. Pre vious results (J.A. Farrar, A.J. Thomson, M.R. Cheesman, D.M. Dooley a nd W.G. Zumft, FEES Lett., 294 (1991) 11) indicated that two binuclear centers are present: a Cu-A-type center and another center designated Cu-Z. These sites display distinct reactivities towards exogenous lig ands. Azide and chloride appear to bind to the Cu-A centers but do not perturb the spectral features of the Cu-Z site that are detectable in the semi-reduced state of the high-activity form of nitrous oxide red uctase. Azide appears to coordinate to at: feast one of the copper ion s in an altered (Cu-Z) site, present in the low-activity form of nitr ous oxide reductase. Nitric oxide perturbs the absorption and circular dichroism spectra attributed to the Cu-Z site, suggesting that NO rea cts directly with this site.