This phenomenon is known as catabolite repression. Xylanase is a secondary metabolite controlled through gene-specific induction and carbon catabolite repression. Endogeneously, it is a catabolite of phenylalanine. Environmental stresses such as antibiotics and catabolite repression can influence toxin expression. Super Optimal broth with Catabolite repression (SOC) is SOB with added glucose. Mal regulon is regulated by catabolite activator protein in a novel manner. Later, she discovered another factor that boosts catabolite repression (catabolite modulator factor, or CMF). Further, high levels of glucose inhibit transcription, since glucose acts as a catabolite repressor. Absence of glucose will "turn off" catabolite repression. Picolinic acid is a catabolite of the amino acid tryptophan through the kynurenine pathway. In 1967 she showed that cAMP reverses catabolite repression in the bacterium "E. coli". The catabolite repression in this case is achieved through the utilization of phosphotransferase system. Some of them, including UV5, has lost catabolite repression at the CAP site. Catabolite Control Protein A (CcpA) is a master regulator of carbon metabolism in gram-positive bacteria.