Protein polymorphism isozymes

It is now recognised that a substantial number of proteins, especially enzymes, are polymorphic in that they exist in the cell as multiple molecular forms differing in certain of their physico-chemical properties. Each form of a polymorphic enzyme is called an isoenzyme or isozyme. Electrophoretic techniques provide convenient methods whereby this protein heterogeneity can be investigated and the approach has been widely exploited to characterise parasites. In short, aqueous parasite extracts are electro-phoresed, or focused isoelectrically, and separated proteins are stained generally (usually with Coomassie Blue) or more specifically with a histochemical (enzyme) stain (the zymogram technique). Further details of individual procedures and the use of the approach in parasite identification are to be found in a number of recent reviews (104,258,413,536,615,856). 

Isozymes are enzyme variants that catalyze the same reaction but are structurally different (they are coded by separate gene loci). Allozymes are variants that arise due to polymorphism at a single gene locus. Isozymes can vary enormously in their properties (e.g., substrate affinities, responses to allosteric effectors, phosphorylation by protein kinases) to support the different functional needs for a particular reaction in different organs or different compartments of the cell (e.g., mitochon-... 

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