The catabolite inactivation of Aspergillus nidulans isocitrate lyase occurs by specific autophagy of peroxisomes

In Aspergillus nidulans, activity of the glyoxylate cycle enzyme isocitrate lyase is finely regulated. Isocitrate lyase is induced by growth on C2 com pounds and Long-chain fatty acids and repressed by glucose. In addition, ac tivity of isocitrate lyase is subject to a second mechanism of catabolite c ontrol, glucose-induced inactivation. Here, we demonstrate that the catabol ite inactivation of A. nidulans isocitrate lyase, a process that takes plac e during glucose adaptation of cells grown under gluconeogenic conditions, occurs by proteolysis of the enzyme. Ultrastructural analyses were carried out in order to investigate the cellular processes that govern the cataboli te inactivation of this peroxisomal enzyme. Addition of glucose to oleate-i nduced cells triggered the specific engulfment and sequestration of peroxis omes by the vacuoles. Sequestration of various peroxisomes by a single vacu ole was a frequently observed phenomenon. Results obtained by immunoelectro n microscopy using antibodies against A. nidulans isocitrate lyase showed t hat degradation of this peroxisomal enzyme occurred inside the vacuole. In addition, ultrastructural studies demonstrated that microautophagy was the autophagic pathway involved in degradation of redundant peroxisomes during glucose adaptation of oleate-induced cells of A. nidulans.