Like Saccharomyces cerevisiae, Candida utilis IGC 3092 has two hexokinases. Their kinetic behavior suggests that they are slightly different from those of S. cerevisiae, and although they are insensitive to xylose, they are affected by trehalose 6-P and ADP. Unlike some other yeast species, C. utilis hexokinases do not show a higher activity under repressing conditions but exhibit a constant fructose/glucose phosphorylation ratio (F/G) in any conditions used. It seems that hexokinase activities are not regulated in parallel with eatabolite repression in this strain [1]. A spontaneous mutant (SDM-1), deregulated for ~-glucosidase and with the glucose proton symport and invertase partially derepressed, was tested for its hexokinase regulation and compared with the wild-type (WT) strain. Studies done in crude extracts under optimum conditions (pH 8 and 30 ~ showed no difference between the two strains in the overall activity and F/G ratio [2]. However, a more detailed work under physiological conditions (pH 7 and 28 ~ showed the F/G ratio in the wild-type strain to be similar as under optimum assay conditions while the F/G ratio found in SDM-1 changed slightly to < 1; this happens at a higher degree also in derepressed S. cerevisiae [3]. As expected, kinetic experiments with glucose and fructose showed a sole apparent Km at high ATP concentration in wild-type crude extracts whereas biphasic kinetics was obtained in the mutant strain. Statistical analysis did not provide conclusive results on the existence of at least two systems with different affinities in the mutant. Responses to xylose and trehalose 6-P were the same for both WT and mutant hexokinases. However, the inhibition by ADP in the mutant was lower than in the WT. All these results suggest that the mutant has altered hexokinases. It is not clear if the alteration is the cause of the derepression or if it represents another failure in the pleiotropic derepressed mutant. The derepression did not translate into significant changes of the main kinetic parameters of batch culture growth on different substrates and different disolved oxygen concentrations. SDM-1 cultures growing on a maltose-glucose mixture consumed these sugars simultaneously, while the ethanol level in the medium remains low. In contrast, the WT shows a sequential sugar consumption, with ethanol production directly associated with glucose consumption. After its exhaustion, ethanol is rapidly uptaken up and a secondary, lower ethanol release is measured in the maltose phase. Maltose is not consumed by the WT until the ethanol concentration in the medium drops. This is predicted by the current explanation of the Kluyver effect, which relates the lack of maltose consumption to the toxic effect of ethanol [4]. The ability to ferment maltose was reported as negligible in other Candida utilis strains; however, the level of ethanol usually stays below 1 mmol/L, a concentration considered nonfermentative [4].