Hexokinase is highly sensitive to T6P could be explained by the presence of a T6P insensitive glucokinase constituting roughly 80% of the glucose phosphorylating capacity of this yeast. A similar explanation might also apply for the phenotype AbMole Indinavir sulfate described for a tps1 mutant of Hansenula polymorpha a yeast in which glucokinase and hexokinase are present during growth in glucose. The levels of metabolites in the disrupted strain are in accordance with the lack of effect of the mutation on the growth in glucose. A slight increase in ATP concentration was measured in the Yltps1 mutant, a finding that parallels the results obtained for a tpsA disruptant of A. nidulans. With our current knowledge no clear explanation for these results can be advanced. Due to the “turbo design” of glycolysis a regulation of the initial steps of the pathway is necessary. In mammals glucose-6-phosphate controls hexokinase and in S. cerevisiae T6P plays a similar role. Yeasts or fungi in which lack of T6P does not affect growth in glucose shall possess other mechanisms to regulate the first steps of glycolysis. It may be asked for the significance of the T6P inhibition of hexokinase in those AbMole Pyriproxyfen organisms in which it appears not to play a significant role in the control of glycolysis. One possibility is that it may serve to control a yet unrecognized function of hexokinase, another one is that it is a consequence of the protein structure shared by most hexokinases and that organisms with a high glycolytic flux have taken advantage of it to control the first irreversible step of glucose metabolism. In Y. lipolytica differences in kinetic and regulatory properties of important glycolytic enzymes like phosphofructokinase or pyruvate kinase indicate that this yeast regulate glycolysis differently from S. cerevisiae. The decrease in sporulation observed in homozygous tps1 diploids parallels findings with tps1 mutants in other fungi like S. cerevisiae Cryptococcus neoformans or Stagonospora nodorum. In S. cerevisiae, the defect has been adscribed to a low expression of MCK1 an inducer of the gene IME1 whose expression triggers sporulation. The low level in Yltps1 diploids of mRNA corresponding to gene YALI0D20966 that appears to be the Y. lipolytica homolog of ScMCK1 will suggest a similar mechanism for the decreased sporulation in this yeast and that the relationship between TPS1 and sporulation was already present in an ancient yeast like Y. lipolytica. Trehalose in Y. lipolytica in different conditions was below 1 nmol/mg dry weight. Disruption of a gene encoding a putative neutral trehalase or overexpression of YlTPS1 increased trehalose content. A similar situation occurred in vascular plants in which trehalose was thought to be absent; incubation with validamycin A, an inhibitor of trehalase, showed the existence of the disaccharide. Hydrolysis of trehalose by trehalase and a low level of Tps1 activity may be responsible for the low levels of the sugar in Y. lipolytica.