CYTOCHROME PIGMENTS OF BAKER'S AND BREWER'S YEASTS

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Abstract
Baker's yeast, grown aerobically, has five absorption bands in the visible spectrum, due to cytochromes a and as at 605 mμ., cytochrome b at 565 and 530 mμ. and cytochrome c at 550 and 523 mμ. Brewer's yeast, anaerobically grown, can have up to three bands due to cytochrome a1 at approx. 590 mμ. and cytochrome b, at 558 and 530 mμ. Baker's yeast under anaerobic conditions becomes indistinguishable from brewer's yeast. Brewer's yeast grown aerobically becomes indistinguishable from baker's yeast and shows cytochromes a and a3, b and c. Cytochromes a, and b1 are said to be precursors in the biosynthesis of cytochromes a and a1, b and c A brewer's yeast incubated at 37° C. lost the cytochrome bands for a, and b1 and developed two new bands at 583 mμ. and 549 mμ. The compounds producing bands at 583 and 549 mμ. may be of biosynthetic importance because of their similarity to the spectra of compounds already reported in yeast, viz., haemoglobin and cytochrome c. Baker's yeast decreased in Qo2 value during fermentation but there was a rise in ability to produce carbon dioxide. The change in cytochrome constitution during anaerobiosis leaves a yeast with a low oxygen uptake. The ability to take up oxygen at all is probably only possible because of a reserve respiration system incorporating cytochromes a1 and b1.