Induction, catabolic enzymes

There may be a limiting substrate concentration required for induction of the appropriate catabolic enzyme. At low substrate concentrations the necessary enzymes wonld simply not be synthesized, and this could be the determining factor in some circumstances (Janke 1987). 

Induction of catabolic enzymes by growth with structurally unrelated substrates... 

Bogdanovic N, Bretillon L, Lund EG, Diczfalusy U, Lannfelt L, et al. 2001. On the turnover of brain cholesterol in patients with Alzheimer s disease. Abnormal induction of the cholesterol-catabolic enzyme CYP46 in glial cells. Neurosci Lett 314 45-48. 

Biotin deficiency in experimental animals is teratogenic, and a number of the resultant birth defects resemble human birth defects. Up to half of pregnant women have elevated excretion of 3-hydroxy-isovaleric acid (Section 11.4), which responds to supplements of biotin, in the first trimester, suggesting that marginal stams may be common in early pregnancy and may be a factor in the etiology of some birth defects. This may be the result of increased catabolism of biotin as a result of steroid induction of biotin catabolic enzymes there is increased excretion of bisnorbiotin and biotin sulfoxide (Zempleni and Mock, 2000a Mock et al., 2002). 

The Induction of Catabolic Enzymes by Preexposure to an Analogue Substrate... 

Experimental aspects of the elective enrichment procedure are discussed in some detail in Chapter 5, but the question of its existence and significance in natural populations already exposed to xenobiotics is conveniently addressed here. It is important to distinguish between induction (or derepression) of catabolic enzymes and selection for a specific phenotype. The former is a relatively rapid response, so that exposure of samples from uncontaminated areas to xenobiotics for a period of weeks or months would be expected to result in the selection of organisms with degradative potential... 

We isolated from the pond two strains of bacteria able to grow on PNP. One of the strains, a Pseudomonas. undergoes an extended lag period under certain conditions in the laboratory. We are currently studying this strain to obtain information about its metabolic pathway for PNP, and the factors that regulate induction of enzymes and growth. Preliminary results indicate that the time required for induction of catabolic enzymes is inversely related to both the concentration of cells and the PNP concentration. The mechanism of such effects is unknown. 

The subsequent induction of enzymes which belong to one metabolic pathway by the products of preceding enzymes (sequential gene expression), is a characteristic of catabolic pathways in bacteria. Although sequential formation of secondary products and secondary metabolic enzymes in many plants and microorganisms has been observed the direct influence of secondary products on the expression of enzymes catalyzing their further transformation has been demonstrated in very few organisms. 

The discovery of the cyclic AMP receptor protein (CAP) in E. coli is most intriguing because it further illustrates the complexities of gene expression even in a relatively uncomplicated system. In E. coli, cyclic AMP stimulates the elaboration of catabolic enzymes involved in the breakdown of arabinose and maltose [184, 185]. A mutant of E. coli has been found that fails to grow on maltose and arabinose. The mutants lack a protein receptor for the cyclic AMP which is believed to bind probably to DNA, but possibly to RNA, which must be present for the induction of the catabolic enzymes. It has also been shown that in order to secure optimal transcription of the lac operon (see below), both the inducer—for example, isopropyl thio-galactoside—and cyclic AMP must be added. 

Induction refers to the stimulation of the synthesis of a catabolic enzyme, which is not currently being made by the cell, by the presence of its substrate or a substrate analogue (a substance closely related to the substrate). Repression refers to the inhibition of the synthesis of an enzyme involved in an anabolic pathway when its reaction product reaches a sufficiently high concentration. The two classical examples of induction and repression in E. coli are the lac operon and the trp operon respectively. 

The cytotoxicity of these analogs for cancer cells has been mainly ascribed to the induction of the catabolic enzymes or to the reduction in activity of the... 

Enzymes for the metabolism of 1,2,4-benzenetriol are also induced in cells of the Moraxella grown on 4-nitrophenol, but there is no evidence that hydroquinone can be converted to 1,2,4-benzenetriol. However, the induction of enzymes for catabolism of... 

Liu, C., Russell, R.M., and Wang, X.D., Exposing ferrets to cigarette smoke and a pharmacological dose of beta-carotene supplementation enhance in vitro retinoic acid catabolism in lungs via induction of cytochrome P450 enzymes, J. Nutr., 133, 173, 2003. 

Other- Liver disease with impaired hemostasis severe renal disease. Hyperlipidemia Heparin may increase free fatty acid serum levels by induction of lipoprotein lipase. The catabolism of serum lipoproteins by this enzyme produces lipid fragments that are rapidly processed by the liver. Patients with dysbetalipoproteinemia (type III) are unable to catabolize the lipid fragments, resulting in hyperlipidemia. 

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