Lactic isoenzymes

Another interesting sperm specific antigen is lactic dehydrogenase-x (LDH-x or LDHC, an isoenzyme of LDH confined to male germ ceUs. 

Blood transfusions can also lead to misleading laboratory values. Stored blood bank blood can appreciably increase the blood ammonia levels (PIO). Blood stored 7 days has been found to contain over 1100 /xg/ml. A case has been reported of a patient receiving massive blood transfusions whose serum contained an additional lactic dehydrogenase isoenzyme (a splitting of the LDH-1 band). The authors concluded that the extra band was not an artifact, but rather represented an abnormal H subunit present in one or more of the transfused plasmas (F6). 

KlO. Kreiitzer, H. H., and Fennis, W. H. S., Lactic dehydrogenase isoenzymes in blood serum after storage at different temperatures. Clin. Chim. Ada 9, 64-68 (1964). 

Enzyme names apply to a single catalytic entity, rather than to a series of individually catalyzed reactions. Names are related to the function of the enzyme, in particular, to the type of reaction catalyzed. This convention implies that one name may, in fact, designate a family of enzymes that are slightly different from each other yet still catalyze the same reaction. For example, lactate dehydrogenase (LDH) has five such isoenzymes in humans. LDH catalyzes the oxidation of L-lactic acid by... 

While each of the five LDH isoenzymes catalyzes the conversion of lactic acid to pyruvic acid, the isoenzymes are produced in different organs. Because of this, the polypeptide moieties and the rates at which lactate can be converted to pyruvate are slightly different for each isoenzyme. Similarly, different species often possess identical metabolic pathways, and have equivalent but slightly different enzymes that catalyze identical reactions. The differences that occur within such a family of enzymes usually occur in noncritical regions of the polypeptide moiety, by the substitution of one amino acid residue for another, or by the deletion of amino acid residues. 

Schapira, F., Dreyfus, J. C., and Schapira, G., Fetal-like patterns of lactic dehydrogenase and aldolase isoenzymes in some pathological conditions. Emymol. Biol. Clin. 7, 98-108 (1966). 

The separation of the isoenzymes of lactic dehydrogenase (LDH) in blood serum. 

Isoenzymes (or isozymes) are multiple forms of an enzyme that differ from each other in such properties as substrate affinity, maximum activity, or regulatory properties. They may be found in different tissues or portions of the same cell. For example, thymidine kinase catalyzing phosphorylation occurs as two isoenzymes—one in the cytoplasm and the other associated with the mitochondria of the same mammalian cell. Lactic dehydrogenase, which catalyzes the reduction of pymvic acid to L-lactic acid exists in five isozymic forms. These are tetramers formed by the association of two polypeptides of equal size H (heart) and M (muscle). 

See also LDH Isoenzymes, Pyruvate/Lactate/Ethanol Metabolism, Anaerobic Process for Generating Metabolic Energy, Lactic Acid Fermentation, Ethanol Metabolism and Gluconeogenesis... 

This inhibitor can even discriminate between isoenzymes. Thus, whereas it irreversibly inhibits the lactic dehydrogenase of skeletal muscle, it does not affect that of the heart. A related compound, 5-(phenoxycarbonylamino)salicylic acid, irreverisbly inhibits the heart (but not the skeletal) isoenzyme, whereas its 4-isomer irreversibly inhibits the skeletal (but not the heart) isoenzyme (Baker and Patel, 1964 Baker, 1967). 

C. Additional serum tests Lactic acid dehydrogenase, lactic acid dehydrogenase isoenzyme, protein determination, and protein electrophoresis. 

Serum proteins lactic acid dehydrogenase-isoenzymes Serum proteins haemoglobin... 

Affinity chromatographic purification 243 of lactic acid dehydrogenase Isolation of lactate dehydrogenase 191 isoenzyme X by affinity chromatography... 

Isoenzymes and analogous enzymes. Many apparently pure enzymes have been separated by electrophoresis into a small number of pure proteins each of these isoenzymes has a specificity similar to that of the crude enzyme, yet differing subtly in physical properties. One of the best-known examples, lactic dehydrogenase (LDH), exists in animal tissues as five isoenzymes. These are tetramers, formed by the association of two polypeptides A and B, and have the following composition , AB3, AgB, A3B, and A. Creatine... 

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