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Discussion on the existence of disaccharide-specific zymase systerns appears to be enitering a new phase. The fermentative breakdown of maltose, sucrose, lactose and trehalose has been investigated in recent years from different directions. Nevertheless, the question whether hydrolysis is an indispensable preliminary to the fermentation of a disaccharide is still variously answered. Supporters of the view that disaccharide fermentation may be 'direct' have as a rule been content, hitherto, with negative proofs showing that oligases are not indispensable to disaccharide fermentation. There is clearly need, however, for a positive hypothesis concerning the mechanism whereby disaccharides could be fermented directly. * Cf. preliminary note [Leibowitz & Hestrin, 1940], earlier investigation [Leibowitz & Hestrin, 1939], and dissertation by Hestrin [1941]. ( 772 ) DIRECT MALTOSE FERMENTATION long as b continues to set the pace, the presence of specific activators or inhibitors of maltolysis will not affect the rate of gas liberation.(3) Vm/ Vg> 1. The simplest explanation of this case is to assume that a exists and that its velocity is greater than a', the latter being rate limiting for glucolysis but not for maltose fermentation. This interpretation is only necessary, however, under certain conditions. Their specification will not be necessary in the present connexion. As in case (2) the limiting part-reaction of maltose fermentation may be contained in b. While the latter remains limiting, specific activators and inhibitors of maltose fermentation need not necessarily affect the rate of gas liberation. Conditions as specified under (1) were found in baker's yeast; conditions as specified under ( 2) and (3) in a brewer's yeast. Methods Yeast. Except where otherwise stated, the yeast used for tests was a Palestinian brand of commercial baker's yeast supplied by Paca Ltd. Samples purchased at different dates were left to stand on ice for a number of days before use. This treatment lessened the fermentative power of the yeast to maltose, augmented the effect on maltose fermentation of exposure of the yeast to glucose, and enhanced certain inhibitory effects described in the sequel. Autofermentation was always found to be negligible. Samples of brewer's yeast, Rishon strain, were kindly provided by Dr Hayman of Palestine Brewery Ltd., Rishon.Sugars. All sugars used were of good quality and supplied by B.D.H. or Schering-Kahlbaum.Gasometers. Except where otherwise stated, fermentation was followed gasometrically using the apparatus described by Hestrin [1941]. Duplicate fermentation runs with this apparatus yielded results which were identical to within 3 %. Aqueous 30 % CaCl2

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