TREHALOSE PHOSPHORYLASE FROM PICHIA FERMENTANS AND ITS ROLE IN THE METABOLISM OF TREHALOSE

During a screening for novel microbial trehalose phosphorylase three P ichia strains were identified as producers of this particular enzyme t hat have not yet been described. To our knowledge, this is the first t ime that this enzyme activity has been shown in yeasts. Pichia ferment ans formed trehalose phosphorylase when cultivated on a growth medium containing easily metabolizable sugars such as glucose. Addition of Na Cl (0.4 M) to the medium increased the synthesis of the enzyme signifi cantly. Production of trehalose phosphorylase was found to be growth-a ssociated with a maximum of activity formed at the transition of the e xponential to the stationary phase of growth. Trehalose phosphorylase catalyzes the phosphorolytic cleavage of trehalose, yielding glucose 1 -phosphate (glucose-1-P) and glucose as products. In vitro the enzyme readily catalyzes the reverse reaction, the synthesis of trehalose fro m glucose and glucose-1-P. For this reaction, the enzyme of P, ferment ans was found to utilize alpha-glucose-1-P preferentially. A partially purified enzyme preparation showed a pH optimum of 6.3 for the synthe sis of trehalose. The enzyme was found to be rather unstable; it was e asily inactivated by dilution unless Ca2+ or Mn2+ were added. This ins tability is presumably caused by dissociation of the enzyme. In contra st to other yeasts, P. fermentans rapidly degraded intracellularly acc umulated trehalose when the carbon source in the medium was depleted. Trehalose phosphorylase seems to be a key enzyme in the degradative pa thway of trehalose in P. fermentans. Additional enzymes in this catabo lic pathway of trehalose include phosphoglucomutase, glucose-6-phospha te dehydrogenase, and gluconolactonase.