Constitutive biosynthesis and localization of alcohol oxidase in the ethanol-insensitive catabolite repression mutant ecr1 of the yeast Pichia methanolica

The activity and localization of alcohol oxidase (EC 1.1.3.13) have been st udied in the Pichia methanolica mutant ecr1 defective in ethanol-induced ca tabolite repression of enzymes of methanol utilization. Ultrastructural, im munocytochemical, and biochemical analyses revealed the presence of peroxis omes containing active alcohol oxidase in the mutant grown in media with me thanol, ethanol, and a mixture of both substrates. No alcohol oxidase was d etected in the wild-type cells (ECR1) grown on ethanol-containing media. Mu tant ecr1 growing in medium containing a mixture of different alcohols and the wild-type strain growing on methanol demonstrated similar buoyant densi ty of peroxisomes (1.24-1.27 g/cm(3)) during isopicnic centrifugation of th e organelles in sucrose density gradients. The integrated genetic, immunocy tochemical, and biochemical data are in agreement with the model that synth esis, translocation into peroxisomes, and assembly of alcohol oxidase in P. methanolica may not require any regulatory signals induced by methanol.