Study of the Assimilation of Proline by Brewing Yeasts

The problem of the incomplete assimilation of proline by brewing yeasts has been approached by studying growth on synthetic media under various conditions, by examining a catabolic reaction which could explain non-degradation under anaerobic conditions and by following the penetration of l-14C proline into the yeast cells. Demonstrations have been made that proline oxidase, the enzyme responsible for the first catabolic reaction of l-proline, requires the participation of cytochrome c to operate and therefore needs the presence of molecular oxygen, and that the permease responsible for the transport of proline is, under normal brewery conditions, repressed by other amino acids of wort. Permease derepression, which should normally occur after the complete consumption of the other amino acids, is made impossible because of the strong anaerobic conditions achieved at that stage.