EFFECT OF DIGITONIN ON MEMBRANE-BOUND AND CHITOSOMAL CHITIN SYNTHETASE-ACTIVITY IN PROTOPLASTS FROM YEAST-CELLS OF CANDIDA-ALBICANS

The effect of digitonin on chitin synthetase present in membrane (MMF) and cytoplasmic fractions (chitosomes) (CF) from C albicans yeast pro toplasts has been determined. The zymogen is preferentially, but not e xclusively, solubilized by digitonin from MME Centrifugation of distin ct solubilized preparations, containing either zymogen, in vivo active enzyme and/or trypsin activated enzyme, on linear sucrose gradients s uggests that both zymogen and trypsin activated enzyme sediment slight ly slower than the active enzyme, pointing out differences between the activation processes in vivo and in vitro or, alternatively, that bot h enzyme activities (active in vivo and zymogenic) correspond to diffe rent gene products. The detection of a zymogenic activity under certai n conditions (0.5 mg ml-1 of digitonin and 64 mug ml-1 of trypsin) als o suggests the existence of more than one pool of zymogenic enzyme in the MMF. Digitonin sensitizes the chitosomal (CF) proenzyme to trypsin : activation is enhanced by low digitonin concentrations in the presen ce of 8 mug ml-1 of protease, whereas activity strongly decreases in t he presence of 64 mug ml-1 of trypsin. Digitonin does not produce zymo gen activation per se in absence of exogenous protease. Furthermore, c hitosome structure is modified into particles with low buoyant densiti es.