Altered control of chorismate mutase leads to tryptophan auxotrophy in Pichia guilliermondii

Abstract

AbstractWe isolated a tryptophan auxotrophic mutant strain, PK101, of Pichia guilliermondii. Its auxotrophy is not caused by a defect in any of the tryptophan biosynthetic enzymes, but its chorismate mutase, an enzyme of the phenylalanine‐tyrosine biosynthesis, is changed. In comparison to the wild type chorismate mutase, the enzyme of PK101 is characterized by a complete loss of sensitivity to L‐phenylalanine inhibition and to a considerable loss of sensitivity to L‐tryptophan activation. Furthermore, the chorismate mutase activity of the mutant is more than 7‐fold higher in the absence of L‐tryptophan than in the wild type. The PK 101 enzyme is also changed in the pH optimum and in some kinetic constants. We found an increased intracellular pool of both phenylalanine and tyrosine, and a reduced content of tryptophan in the mutant cells. Our genetic data indicate that the mutant phenotype is dominant over the wild type.