酶催化与调控英文版.pptVIP

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * 13.7 Amount of some enzymes are increased when certain inducers (often enzyme substrates) are present in the cells. 13.7.1 This is often seen in bacterium cells. 13.7.2 The presence of lactose in a culture medium induces a large increase in the amount of b-galactosidase (and two other enzymes, galatoside permease and thiogalactoside transacetylase) 学习文档 13.8 Both the synthesis and degradation of the certain important enzymes are tightly controlled. For example, in cell cycle control and in cancer. Either overexpression or overproduction of a protein or a failure to turn off and destruct a protein can lead to cancer. 学习文档 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 学习文档 学习文档 学习文档 木糖 学习文档 Glycolysis: 糖原酵解 学习文档 学习文档 学习文档 13. The enzymatic activity of some enzymes are precisely and tightly regulated in living organisms to meet physiological requirements. 13.1 Allosteric enzymes (similar to hemoglobin) are regulated by reversible, noncovalent binding of modulators (often being metabolites). 13.1.1 Feedback inhibition, i.e., building up of a pathway’s end product ultimately slows the entire pathway, is often realized through allosteric enzymes. 13.1.2 The enzyme catalyzing the first step of a synthetic pathway is often an allosteric enzyme. 学习文档 13.1.3 For example, threonine dehydratase in the Ile synthesis pathway, and aspartate transcarbamoylase (ATCase, the best understood allosteric enzyme) in the pyrimidine nucleotide synthesis pathway. 13.1.4 The modulators usually bind not to the active site but to another specific regulatory site. 13.1.5 The enzyme activity varies when the concentration of the modulators vary, hence the synthesis pathway is open only when the end product is lacking (closed when the end product is abundant). 学习文档 学习文档 学习文档 13.2 Allosteric enzymes do not follow the Michaelis-Menton kinetics. 13.2.1 They do exhibit saturation effect, but do not show a hyperbolic curve