Compartmentation, of enzymes

Edwards, G.E., Foster, J.G. Winter, K. (1982). Activity and intracellular compartmentation of enzymes of carbon metabolism in CAM... 

There are two forms of the enzyme carbamoyl phosphate synthetase, one in the mitochondrial matrix and the other in the cytoplasm. What might be the consequence and role of this so-called compartmentation of enzymes ... 

Spilatro, S. R., and Preiss, J. 1987. Regulation of starch synthesis in the bundle sheath and mesophyll of Zea mays L. Intercellular compartmentalization of enzymes of starch metabolism and the properties of the ADPglucose Pyrophosphorylases. Plant Physiol. 83, 621-627. 

As for the first question cytoskeletal interactions are apparently involved in keeping the proteinases and their transmembrane substrates apart, keeping them in distinct domains of the plasma membrane. See also ref. 15. Upon activation, the cytoskeletal attachments seem to be loosened so that the proteinases and their substrates can approach each other and interact. How spatial restriction and compartmentalization of enzymes and substrates controls their action is of more general importance. We shall come back to that (Chapter 7). 

During the light period, when COi is being fixed in the chloroplasts by the RPP pathway, it is likely that the mechanisms discussed above for C3 photosynthesis are also functional in CAM plants [19]. Additional control mechanisms are expected to provide for the efficient functioning of the diurnal cycle of CO2 fixation. The functioning of CAM cannot, however, be interpreted solely in terms of enzymolo-gy, but rather will involve cellular compartmentation of enzymes and metabolites together with intracellular transport processes [17]. 

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. 

In leaves at early stages of development, extractable invertase activity (measured at its pH optima) can exceed extractable sucrose synthase activity by 10 to 20 fold (15). yet compartmentalization of enzyme and substrate may make the relative flux through these parallel paths quite different from... 

Each cellular component has its unique physiological function(s)/metabolic activity. Certain enzymes are found to be present either exclusively or predominantly in certain subcellular organelles and can be used as enzyme markers for the characterization of these cellular componeuts. Compartmentalization of enzymes in subcellular organelles is summarized in Table 3.2. 

C- plants (9). One of the features of C. plants, is the presence of "Kranz" anatomy. There is compartmentalization of enzymes in "Kranz" anatomy viz PEPC in the cytosol of mesophyll cells and RuBISCO in the chloroplasts of the bundle sheath cells(ll). Accordingly in the present study, predominent activity of PEPC in the partially green maize callus cultures and lowest portion of young leaf lacking well developed chloroplasts can be explained. 

Enzyme studies 1. Substrate specificity and rates, along with inhibitor studies to facilitate study of detailed mechanisms 1. No account of accessibility and cellular compartmentalization of enzymes... 

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