Reactions of P582 from Desulfotomaculum nigrificans with substrates, reducing agents and carbon monoxide

Abstract

Desulfotomaculum nigrificans contains a CO-binding pigment (P582) which may be responsible for sulphite, hydroxylamine and nitrite reduction in this organism. In crude extracts P582 reacted with NaBH 4 or Na 2S 2O 4 as evidenced by a decrease in absorbance at 582 nm. The extent to which P582 reacted with NaBH 4, but not Na 2S 2O 4, diminished progressively during purification of the pigment. In the presence of Na 2So 3, however, NaBH 4 caused a decrease in the absorbance of the purified pigment at 582 nm and the appearance of an absorbance maximum in the region of 610 nm: a CO complex was also formed in the presence of CO, NaBH 4 and Na 2So 3. Similar spectral changes in the presence and absence of CO, were produced by dithiothreitol and reduced methyl viologen although not at equal rates. It is concluded that the spectral changes were a consequence of reduction of P582 and did not reflect specific interactions between the chromophore and sulphur compounds. Methyl viologen-reduced P582 appeared to be reoxidized by Na 2So 3 and NH 2OH. KNO 2 or NO reacted with reduced P582 and a spectrum with an absorbance maximum at 593 nm was obtained.