Heterogeneous systems membrane enzymes

These properties are likely to have an important influence on the behavior of intact biochemical systems, e.g., within the living cell, enzymes do not function in dilute homogeneous conditions isolated from one another. The postulates of the Michaelis-Menten formalism are violated in these processes and other formalisms must be considered for the analysis of kinetics in situ. The intracellular environment is very heterogeneous indeed. Many enzymes are now known to be localized within 2-dimensional membranes or quasi 1-dimensional channels, and studies of enzyme organization in situ [26] have shown that essentially all enzymes are found in highly organized states. The mechanisms are more complex, but they are still composed of elementary steps governed by fractal kinetics. 

Membrane reactors using biological catalysts can be used in enantioselective processes. Methodologies [78] for the preparation of emulsions (sub-micron) of oil in water have been developed and such emulsions have been used for kinetic resolutions in heterogeneous systems catalyzed by enantioselective enzyme (see Fig. 9.6). A catalytic reactor containing... 

Along with relatively simple cases of reactions involving catalysts whose concentration can be assessed from the adsorption isotherm, reactions are known to occur in the oil/water system in which the membrane enzyme system acts as a catalyst of a heterogeneous process if it adheres to the interface [9, 10, 12, 19]. 

Our work deals with the necessity of creating kinetics laws for heterogeneous enzymology. There was a big gap between the classical enzyme kinetics in solution and highly structured biological systems. All the concepts of diffusion reaction are clear for our thick membrane but are also useful for lipid-protein membranes, even if the process of transport is not only classical diffusion. 

Intracellular nucleotides play an important role in enzyme and ion channel regulation as well as in energy metabolism and nucleic acid synthesis. There is now widespread appreciation that ATP (and other nucleotides) may so be released into the extracellular fluid by exocytosis from nerve terminals or secretory cells. Thus, extracellular ATP can act as a neurotransmitter or modulator in a variety of peripheral tissues and cells, in autonomic ganglia and in the central nervous system [1-3]. The responses to extracellular ATP are mediated via membrane-bound receptors, termed P2-purinoceptors. Evidence has accumulated indicating heterogeneity of P2-purinoceptors, and it has become apparent that ATP acts on at least five P2-purinoceptor subtypes, i.e. P2X> P2Y> P2U> 2T 2Z... 

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