The carbon monoxide-reactive haemoproteins of yeast

Abstract The yeasts Saccharomyces cerevisiae, Candida utilis and Saccharomyces carlsbergensis were shown to have two CO-binding haemoproteins in addition to cytochrome a 3 . These haemoproteins were separated by a method described. One, contained in the particulate fraction of the cells, was extracted by sodium deoxycholate and precipitated at 30% (NH 4 ) 2 SO 4 saturation. The visible spectrum was that of a B-type cytochrome, but it reacted with carbon monoxide to produce CO-difference transmission minima at 408 mμ, 540 mμ and 572 mμ. It did not form a complex with either CN − or O 2 . The other haemoprotein was separated from the non-particulate cellular fraction and precipitated at 65% (NH 4 ) 2 SO 4 saturation. Like the haemoglobin of blood, this haemoprotein can be oxygenated, reduced and oxidized and can react with CN − and CO. The CO-difference transmission minima are situated at 419 mμ, 532 mμ and 568 mμ. CO-difference reflectance spectrophotometry of C. utilis cells was employed for semi-quantitative estimation of the carbon monoxide complex of cytochrome a 3 (CO- a 3 ) and the CO complex of those haemoproteins with a 570 mμ CO-difference reflectance minimum (CO-Hp 570 ). The concentration of CO- a 3 and CO-Hp 570 varied with glucose concentration and culture age. Evidence is presented for contribution to the CO-Hp 570 of C. utilis by both cytochrome o and haemoglobin in high glucose cultures and by cytochrome o alone in low glucose cultures.