Multienzyme compartmentalization

In bacteria and plants, the individual enzymes of the fatty acid synthase system are separate, and the acyl radicals are found in combination with a protein called the acyl carrier protein (ACP). However, in yeast, mammals, and birds, the synthase system is a multienzyme polypeptide complex that incorporates ACP, which takes over the role of CoA. It contains the vitamin pantothenic acid in the form of 4 -phosphopan-tetheine (Figure 45-18). The use of one multienzyme functional unit has the advantages of achieving the effect of compartmentalization of the process within the cell without the erection of permeability barriers, and synthesis of all enzymes in the complex is coordinated since it is encoded by a single gene. 

A common characteristic of metabolic pathways is that the product of one enzyme in sequence is the substrate for the next enzyme and so forth. In vivo, biocatalysis takes place in compartmentalized cellular structure as highly organized particle and membrane systems. This allows control of enzyme-catalyzed reactions. Several multienzyme systems have been studied by many researchers. They consist essentially of membrane- [104] and matrix- [105,106] bound enzymes or coupled enzymes in low water media [107]. 

Michel P.E., Gautier S.M., Blum L.J., Effect of compartmentalization of the sensing layer on the sensitivity of a multienzyme-based bioluminescent sensor for L-lactate, Anal. Lett. 1996 29 (7) 1139-1155. 

Stafford HA. 1981. Compartmentation in natural product biosynthesis by multienzyme complexes. In Conn EE, Ed. The Biochemistry of Plants. New York Academic Press, Vol. 7 pp. 117-137. 

Srere, P. A. Mosbach, K. (1974). Metabolic compartmentation symbiotic, organellar, multienzymic, and microenvironmental. Ann. Rev. Microbiol. 28,61-83. 

In the cell, compartmentation of enzymes into multienzyme complexes or organelles provides a means of regulation, either because the compartment provides unique conditions or because it limits or channels access of the enzymes to substrates. Enzymes or pathways with a common function are often assembled into organelles. For example, enzymes of the TCA cycle are all located within the mitochondrion. The enzymes catalyze sequential reactions, and the product of one reaction is the substrate for the next reaction. The concentration of the pathway intermediates remains much higher within the mitochondrion than in the surrounding cellular cytoplasm. 

Compartmentation in Natural Product Biosynthesis by Multienzyme Complexes... 

In a wider sense, compartmentation is possible through purely chemical means, e.g. embedding of enzymes in lipid layers and aggregation of enzymes to form multienzyme complexes,... 

Association of enzymes into multienzyme systems and complexes, i. e. metabolic compartmentation. 

Attempts to unravel the problems posed by cell compartmentation are hampered by the extreme difficulty of determining the exact intracellular location of many enzymes, let alone the distribution of metabolites. Even within a compartment distribution may not be uniform. For example, the existence of multienzyme systems, in which each enzyme is adjacent to the next one in the metabolic pathway, limits the diffusion of metabolites from the site of their production. This inequality of distribution of metabolites within the cell makes it difficult to demonstrate in vitro control processes which may occur in vivo. 

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