The absorbance maximum (630 nm) of reduced cytochrome d in Escherichia coli membrane particles was diminished by 160 μM AgNO3 or NaNO3 and accompanied by the formation of a species with an absorption maximum at 640–645 nm. Nitrite, trioxodinitrate and nitric oxide elicited qualitatively similar, but faster, changes in the spectrum of cytochrome d, suggesting that formation of a nitrosyl complex may be involved in all cases. In direct contrast to an earlier report, silver ions (160 υM) were without effect on the α-bands of reduced cytochromes d, b or a 1.
