Cytochrome c ' from Paracoccus denitrificans: spectroscopic studies consistent with a role for the protein in nitric oxide metabolism

Cytochrome c' was purified from the denitrifying bacterium Paracoccus denit rificans and the interaction of the protein with nitric oxide was examined spectroscopically. Two distinct types of haem-nitrosyl electronic absorptio n spectrum were observed, which were dependent upon [NO]. When cytochrome c ' was saturated with NO, alpha and beta bands were centred at 562 nm and 53 0 nm, whereas with sub-saturating concentrations of NO the alpha and beta b ands were red-shifted to 578 nm and 542 nm respectively. Further spectrosco pic analysis showed that purified cytochrome c', added to suspensions of P. denitrificans, is able to complex with the NO which is formed as a freely diffusible intermediate of denitrification. In the presence of added NO(3)( -)or NO2-, 40-60% of Fe(II)-cytochrome c' forms a B-coordinate haem-nitrosy l complex. In the absence of nitrogen oxyanions or NO whole denitrifying ce lls are able to remove the NO from a Fe(II)-cytochrome c'-NO complex. These findings support the hypothesis that the physiological function of this en igmatic cytochrome involves the reversible binding of nitric oxide. (C) 199 9 Elsevier Science B.V. All rights reserved.