CONTENTS OF CYTOCHROMES IN YEAST

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Abstract
The contents of cytochromes in yeast were determined quantitatively from the absorption spectra, using a solid cell paste of intact yeast. During the industrial production of baker's yeast, the contents of the cytochromes, particularly of cytochrome aa3 at successive stages, increased gradually with increasing aeration. In semi-aerobically grown baker's yeast, the contents of cytochromes aa3, b and c were 0·9, 2·9 and 2·9 × 10−5 moles/litre of fresh yeast (total amount 6·7 × 10−5 moles/litre), while in vigorously aerated commercial baker's yeast the respective values were 2·3, 4·8 and 5·2 × 10−5 moles/litre (total amount 12·3 × 10−5 moles/litre). In brewer's yeasts separated after the brewing process, the contents of cytochromes were markedly lower than in baker's yeast grown with limited aeration, whereas in top-fermenting yeast the total cytochrome content, aa3 + b + c, was in some samples markedly higher, 7·1 × 10−5 moles/litre, than in bottom-fermenting brewer's yeast, 2·4 × 10−5 moles/litre. When brewer's bottom yeast was grown on a laboratory scale under increasing aeration, a maximum appeared in the cytochrome contents when aeration was moderate, and increased aeration inhibited the formation of cytochromes. The cytochrome contents in brewer's bottom yeast may exceed the amounts found in commercial baker's yeast. In addition to aeration, the type of metabolism influences the amounts of cytochromes in yeast.