A decrease in the activity of certain auxiliary catabolic enzymes when a surplus of an (easily metabolizable) substrate is available. Commonly this effect is caused by glucose (glucose repression) or by metabolites produced from glucose.
Source:
PAC, 1992, 64, 143. 'Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992)' on page 149 (https://doi.org/10.1351/pac199264010143)