Absence of the Pre-adaptive Utilization of Galactose by Yeasts

Abstract

YEASTS genetically capable of fermenting galactose require a definite period of exposure to galactose before they can utilize it. Reiner and Spiegelman¹ found that immediately after the addition of galactose (recrystallized from alcohol) to a suspension of unadapted cells (capable of adapting themselves to the fermentation of galactose) the cells consumed oxygen and gave off carbon dioxide with a respiratory quotient of about 1. They inferred that this oxidation, which occurred before the cells became adapted to the fermentation of galactose, was due to the presence of a constitutive enzyme controlling the oxidation of galactose, and termed the phenomenon “The Pre-adaptive Oxidation of Galactose”. They proposed that the phenomenon is general and that yeasts completely incapable of fermenting galactose, as well as those only unadapted, are able to oxidize galactose with a respiratory quotient of 1 immediately on exposure. We have found that ordinary C.P. galactose gives a positive iodoform test which suggests that galactose recrystallized from alcohol contains alcohol. Since Reiner and Spiegelman found a respiratory quotient of 1 rather than 0.66 (the respiratory quotient of oxidation of alcohol), it is presumed that, in addition to alcohol, galactose also contains another impurity, presumably glucose.