When a microorganism is provided with a rapidly metabolizable carbon-energy source such as glucose, the resulting increase in the intracellular concentration of ATP leads to the repression of enzyme(s) biosynthesis, thus causing a slower metabolization of the energy source. This phenomenon is known as catabolite repression.
In situations where a microorganism receives a readily metabolizable carbon-energy source such as glucose, an increase in intracellular ATP levels suppresses enzyme synthesis, resulting in reduced metabolic activity of the energy source. This effect is referred to as catabolite repression.