REGULATION OF PHOSPHOTRANSFERASES IN GLUCOSE-FERMENTING AND XYLOSE-FERMENTING YEASTS

This research examined the titers of hexokinase (HK), phosphofructokin ase (PFK), and xylulokinase (XUK) in Saccharomyces cerevisiae and two xylose fermenting yeasts, Pachysolen tannophilus and Candida shehatae, following shifts in carbon source and aeration. Xylose-grown C. sheha tae, glucose-grown P. tannophilus, and glucose-grown S. cerevisiae, ha d the highest specific activities of XUK, HK, and PFK, respectively. X UK was induced by xylose to moderate levels in both P. tannophilus and C. shehatae, but was present only in trace levels in S. cerevisiae. H K activities in P. tannophilus were two to three fold higher when cell s were grown on glucose than when grown on xylose, but HK levels were less inducible in C. shehatae. The PFK activities in S. cerevisiae wer e 1.5 to 2 times higher than in the two xylose-fermenting yeasts. Tran sfer from glucose to xylose rapidly inactivated Wt in P. tannophilus, and transfer from xylose to glucose inactivated XUK in C. shehatae. Th e patterns of induction and inactivation indicate that the basic regul atory mechanisms differ in the two xylose fermenting yeasts.