Isoenzymes identification

R23. Rose, R. G., and Wilson, A. C., Peafowl lactate dehydrogenase Problem of isoenzyme identification. Science 163, 1411-1413 (1966). 

Wagner et. al (46) studied 376 patients to evaluate the importance of identification of the myocardial-specific MB isoenzyme in the diagnosis of acute myocardial infarction. An attempt was made to determine the incidence of falsely positive (mb). No acute infarction was diagnosed in all patients in whom neither total CK nor the isoenzymes of LD indicated myocardial necrosis. Incidence of falsely negative (MB) was zero in 33 patients. They concluded that determination of the isoenzymes of CK provides both a sensitive and specific indication of acute myocardial infarction. 

Bertram PA, RA Schmitz, D Linder, RK Thauer (1994) Tungsten can substitute for molybdate in sustaining growth of Methanobacterium thermoautotrophicum identification and characterization of a tungsten isoenzyme of formylmethanofuran dehydrogenase. Arch Microbiol 161 220-228. 

R. G., Huber, H.E. Identification and characterization of pleckstrin-homology-domain-dependent and isoenzyme-specific Akt inhibitors. 

However, it should be noted that isoenzymes, i.e., different enzymes catalyzing identical reactions, would have the same four-digit classification. The classification system provides only the basis for a unique identification of an enzyme the particular isoenzyme and its source still have to be specified. For example, peroxidases isolated from soybeans and horseradishes have the same classification, i.e., EC 1.11.1.7. Currently, there are approximately 3200 enzymes that have been listed and assigned classification numbers. 

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). 

Dobbs PC, Epstein DL, Anderson PJ. Identification of isoenzyme C as the principal carbonic anhydrase in human ciliary processes. Invest Ophthalmol Vis Sci 1979 18 867-870. 

C tABAREK J, RaYC1K)WI91URY M, Ravid K. Identification and functional characterization of protein kinase C isoenzymes in platelets and HEL cells. JBiol Chem 267 10011-10020,1992. 

O Brien SJ, Shannon JE Gail MH (1980) A melocular approach to the identification and individualization of human and animal cells in culture isoenzyme and alloenzyme genetic signatures. In Vitro 16 119-135. 

In 1968, Fishman and his collaborators reported the identification of an ALP in the serum of a patient with metastatic squamous cell carcinoma of the lung that was biochemicaEy and immunologicaUy identical with the ALP of a normal placenta. The newly discovered isoenzyme was termed the Regan isoenzyme after the patient in whom it was discovered. The Regan isoenzyme has been detected in tumor tissues and in sera of patients with many types of malignant disease and in some patients with nonmalignant diseases. An incidence of the isoenzyme of 3% to 15% in sera of cancer patients has been estimated, but this varies with the sensitivity of the methods used for its detection. Other variant forms of ALP have since been discovered in tumor tissues. These variants show many similarities to normal placental ALP but may differ in other properties, such as response to certain inhibitors. 

Differences in catalytic properties, such as differences in K, , relative rates of reaction with substrate analogues (when the specificity of the enzyme allows for variation in the structure of the substrate), pH optima, and response to inhibitors, typically exist between isoenzymes that are the products of multiple gene loci. These differences can be made the basis of methods of identification and measurement of particular isoenzymes. 

Muramatsu, T., Giri, P.R., Higuchi, S., and Kincaid, R.L. (1992). Molecular cloning of a calmodulin-dependent phosphatase from murine testis Identification of a developmentally expressed nonneural isoenzyme. Proc. Natl. Acad. Sci. 59 529-533. 

Class I aldolases of mammals and other vertebrates can be subdivided into three distinct isoenzymes.143,331 Identification of the parental aldolases A, B, and C has been made from their substrate specificities (ratio of activity towards D-fructose 1,6-bisphosphate and towards D-fructose 1-phosphate), electrophoretic mobilities, tissue distribution, and specific immunological properties. Aldolase A is the major form, present in muscle aldolase B, the predominant form in liver and kidney and aldolase C, present in brain with aldolase A. In tissues where more than one aldolase isoenzyme occurs, a hybrid form is often observed.331... 

Several systems of nomenclature have been adopted by workers in different laboratories for the classification of the human GST isoenzymes. Kamisaka et al. (Kl) originally described five basic (alpha-class) forms of GST in human liver, which were assigned Greek alphabetical symbols (a, p, y, b, and e). Following the identification of neutral (mu-class) GST in liver and acidic (pi-class) GST in placenta, the additional forms were also designed by the Greek symbols p, ij), (]), and Ji (G13, H16, S26, S36, W3). 

Enzyme Standards. Enzyme electrophoresis has proliferated with Increased genetic profiling for medical and forensic use. Standards for enzyme analyses In the form of defined kits containing banks of enzymes of different Isoenzyme patterns are not commercially available. For the most part, forensic laboratories use Individuals from within their own laboratories who have known phenotypes for the enzymes of Interest. Such donors become de facto standards. The Interlaboratory exchange of samples and rigorous continued training In enzyme phenotype Identification will Improve this standards base. 

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