Crystalline pseudomonas cytochrome oxidase: II. Spectral properties of the enzyme

In the crystalline preparation of Pseudomonas cytochrome oxidase, the α-band due to haem a 2 varied in both absorbancy and position with pH when the enzyme was reduced with Na 2S 2O 4. Thus it was at 655 mμ, 629 mμ and 652 mμ, and 625 mμ at pH 7.6, 7.0 and 5.6, respectively. The corresponding γ-band was invariably at 460 mμ. But, when the enzyme was reduced with ascorbate, the α-band did not show dependence on pH. The γ-band due to haem a 2 was very low in absorbancy compared with corresponding α-band. In the presence of cyanide, the α-band due to haem a 2 appeared at 627 mμ and the corresponding γ-band was split into two parts, with maxima at 443 mμ and 472 mμ. In the presence of CO, the α-band due to haem a 2 was very depressed in absorbancy and the corresponding γ-band became invisible. Nitrite and NO had the same effect on Na 2S 2O 4-reduced enzyme. In the presence of these reagents, a peak appeared at 665 mμ, the γ-band at 460 mμ disappeared, and the enzyme solution became reddish brown. With ascorbate-reduced enzyme, a bump at 570 mμ appeared on addition of nitrite or NO. Hydroxylamine had a complicated effect on the enzyme. The reagents mentioned above scarcely affected the absorption spectrum due to haem c of the enzyme.