Anales de Biología

Résumé

Vegetative ceUs of Schizosaccharomyces pombe lack trehaiase activity but the enzyme activity is present at the ascospore stage and later disappears during germination. Cells of a yeast strain unable to sporulate are devoid of trehalase throughout the entire life cycle. The ascospore enzyme is not released to the culture medium and shows the properties of a nonregulatory trehaiase with acidic optimum pH and Km = 10'9x10-'M. On the basis of itsinvivo sensitivity to mild acid treatments and of its behaviour duringfractionation at low speed centrifugation of whole ascospore extracts, the enzyme appears to be externally located on the cells and covalently bound to the cell wall structure. In sifu inactivation of the trehalase enzyme partially blocks the initial morphological changes of germination. Germination of trehalase-less ascospores is further delayed when resynthesis of the enzyme is prevented by addition of cycloheximide. The results suggest that the trehalase enzyme plays a critica1 role in the early events of germination by mobilizing the endogenous trehalose stored in ascospores so that the process can take place even in the absence of externa1 carbon sources directly available provided other nutrients be present. Thus. the trehalose-trehalase system might represent in this yeast a significant mechanism that would allow to initiate germination under conditions in which the energy and carbon supplies in the surrounding medium are poor for the ascospores but could be used for the resulting vegetative cells.