Intracellular protein phosphatase activity has been identified in the yeast Yarrowia lipolytica. This activity was maximal early in its exponential growth phase, and it was enhanced by Pi-deficiency of the culture medium. On a Pi-deficient medium, the major protein phosphatase was purified. This enzyme was dissociated with 80% ethanol treatment, its activity was slightly increased (30%) with heparine and largely enhanced (1.5 to 3-fold) with polycations. This enzyme could be classified as a type 2A protein phosphatase. It is composed of a catalytic subunit and other subunits. Its optimum pH value is 7.2, the apparent Km for casein is 37 μM and the apparent velocity 3.6 pmol hydrolyzed 3 2 Pi min - 1 pmol - 1 enzyme.Une activite proteine phosphatase intracellulaire a ete mise en evidence chez la levure Yarrowia lipolytica. Cette activite est maximale en debut de la phase exponentielle de croissance et augmentee largement lorsque le milieu de culture est appauvri en phosphate. La proteine phosphatase majeure retrouvee sur milieu appauvri en phosphate a ete purifiee. Cette enzyme est dissociee par un traitement ethanolique et son activite est augmentee legerement (30 %) par l'heparine et fortement (150 a 300 %) par les polycations. Il s'agirait donc d'une proteine phosphatase de type 2A, composee d'une sous-unite catalytique et d'autres sous-unites. Son pH optimum est 7,2, son Km apparent pour la caseine 37 μM et la vitesse maximale apparente 3,6 pmol de 3 2 P libere min - 1 pmol - 1 enzyme.