Multiplicity of mechanisms of carbon catabolite repression involved in the synthesis of alcohol oxidase in the methylotrophic yeast Pichia pinus

The effect of various carbon compounds on the synthesis of alcohol oxidase in a medium with methanol was studied in the wild type strain of Pichia pinus as well as in gcr1 and ecr1 mutants defective in glucose and ethanol repression of methanol metabolic enzymes, respectively. Compounds repressing the synthesis of alcohol oxidase in the wild type strain were divided into four groups. Repression of alcohol oxidase by compounds of the first group (glucose, fructose, mannose, galactose, L‐sorbose and xylose) was impaired only in the gcr1 mutant and that by compounds of the second group (ethanol, acetate, 2‐oxoglutarate and erythritol) only in the ecr1 mutant. Repression by compounds of the third group (malate, dihydroxyacetone) was not impaired in both these regulatory mutants and that by compounds of the fourth group (succinate, fumarate, L‐arabinose, sorbitol, salicin, xylitol and cellobiose) was partially reduced in both gcr1 and ecr1 strains. Mutation gcr1 causes a significant decrease in phosphofructokinase activity. It also led to a six‐ to seven‐fold increase in intracellular pools of glucose‐6‐phosphate and fructose‐6‐phosphate and to a two‐fold decrase in the intracellular pool of fructose‐1,6‐bisphosphate. In ecr1 strains, a decrese in 2‐oxoglutarate dehydrogenase activity accompanied by an increae in activities of NAD‐ and NADP‐dependent isocitrate dehydrogenases and NAD‐ and NADP‐dependent glutamate dehydrogenases was demonstrated. The intracellular pool of 2‐oxoglutarate was increased 2·5‐fold in ecr1 strains. Genes GCR1 and ECR1 are not linked. The mechanisms of catabolite repression of alcohol oxidase in methylotrophic yeasts are discussed.