Evidence for catabolite degradation in the glucose-dependent inactivation of yeast cytoplasmic malate dehydrogenase.

The cytoplasmic malate dehydrogenase of Saccharomyces cerevisiae was radioactively labeled during its synthesis on a glucose-free derepression medium. After purification a sensitive radio-immunoassay for this enzyme could be developed. The assay showed that after the physiological, glucose-dependent 'catabolite inactivation' of cytoplasmic malate dehydrogenase an inactive enzyme protein is immunologically not detectable. Together with the irreversibility of this reaction in vivo this finding strongly suggest a proteolytic mechanism of enzyme inactivation. For this process the term 'catabolite degradation' is used.