The action spectrum of hemoprotein oxidase in Nitrobacter agilis

A photochemical action spectrum for the relief by light of the carbon monoxide inhibition of respiration in Nitrobacter agilis (ATCC No. 14123) has been determined by the method of Castor and Chance, the first such determination in a chemolithotrophic organism. The cells were grown at 30 °C in liquid culture, were used when consuming 2–4 mM/ml per day of nitrite, and were concentrated by centrifuging. They respired actively at room temperature for about 3 h in air but only 75 min in the CO:O2 (4:1) mixture. Consistent γ and α bands of a hemoprotein spectrum were obtained from the combined results of two cultures. The maxima are at 432 ± 2 and 592 ± 2 nm; the γ/α height ratio is 6.4 (±22%) and the half-height width of the γ band is 15 nm. Since cytochrome a1 but not a3 has been reported in several Nitrobacter studies, the conclusion is that an a1-type cytochrome is a terminal oxidase in Nitrobacter agilis. The great scatter in the points around the β peak presumably results from the many cultures used, and possibly from differing oxidase activities in different phases of growth. The breadth of the peak could result from the presence of cytochrome o in some cultures. The possibility of more than one terminal oxidase is not excluded.