Fumaric acid overproduction in yeast mutants deficient in fumarase

A nuclear mutant of Saccharomyces cerevisiae deficient in mitochondrial fumarase has been identified through the in vitro biochemical assay of enzyme activity after visual selection due to an increased acidification ability of its colonies. Cells of the fumarase-deficient mutant fermenting glucose accumulated extracellular fumaric acid. This accumulation was observed only in growing cultures and required functional mitochondrial electron transport from succinate dehydrogenase to oxygen.