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Biosynthetic mechanisms are organic reaction mechanisms for the biosynthesis of macromolecules, such as proteins and nucleic acids, as well as mechanisms for the synthesis of metabolites, such as vitamins and steroids (also see metabolism, metabolic pathways). Biosynthetic mechanisms are important for understanding biological transformations at the atomic level. Such knowledge is critical for metabolic engineering and other biological engineering processes.〔P. M. Dewick, Medicinal Natural Products: A Biosynthetic Approach, 3rd Edition (Wiley-VCH, 2009).〕 Multistep enzyme-catalyzed reactions (see enzyme catalysis) are involved in biosynthesis.〔E. Garcia-Junceda, Multi-Step Enzyme Catalysis: Biotransformations and Chemoenzymatic Synthesis (Wiley-VCH, 2008)〕 Biosynthetic mechanisms illustrate the stepwise chemical transformations of how simple molecules are converted to complex products in biological systems. Each individual step in a biosynthetic mechanism consists of starting material, intermediate, and product. These steps are proposed usually based on observation of enzyme intermediates. For example, in the first major step of cholesterol biosynthesis: acetyl-CoA reacted with acetoacetyl-CoA (two starting materials) to generate hydroxylmethyl glutaryl-CoA (HMG-CoA, the product), the reaction is catalyzed by HMG-CoA synthase. The biosynthetic mechanism for this transformation has 3 distinct steps〔Theisen, M. J.; Misra, I.; Saadat, D.; Campobasso, N.; Miziorko, H. M.; Harrison, H. T. D., PNAS 2004, 101, 16442-16447.〕 (Figure): first step is acetylation of enzyme cysteine to generate the thioester intermediate, followed by a Claisen condensation, then the last step is hydrolysis of the condensation product to generate HMG-CoA. Other representative examples of biosynthetic mechanisms include amino acid synthesis, purine metabolism, and citric acid cycle. ==References== * * * * 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Biosynthetic mechanism」の詳細全文を読む スポンサード リンク
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