Enzymes isozymic forms

A detailed scientific study on the properties of the five major isozymic forms of the lignin peroxidases produced in our pilot reactor has recently been published 12), Our purified enzyme in this study is composed of two isozymes having isoelectric points of 3.85 and 3.80 and molecular masses of 42 000. In this study we have characterized the enzyme s stability as an industrial product. 

The enzyme consists of three main isozymes formed by the dimeric combination of two different protein chains. The two types of protein chains have been labelled E (for ethanol active) and S (for steroid active). About 90% of liver alcohol dehydrogenase (LADH)) is EE and the remaining 10% consists of ES and SS. SS is also ethanol active, although lower than ES and EE, and vice versa. Polymeric forms of the isozymes are also known. 

The second messenger molecules Ca2+ and cyclic AMP (cAMP) provide major routes for controlling cellular functions. In many instances, calcium (Ca2+) achieves its intracellular effects by binding to the receptor protein calmodulin. Calmodulin has the ability to associate with and modulate different proteins in a Ca2+-dependent and reversible manner. Calmodulin-dependent cyclic nucleotide phosphodiesterase (CaMPDE, EC 3.1.4.17) is one of the key enzymes involved in the complex interactions that occur between the cyclic-nucleotide and Ca2+ second messenger systems (see Figure 13.2). CaMPDE exists in different isozymic forms, which exhibit distinct molecular and catalytic properties. The differential expression and regulation of individual phosphodiesterase (PDE) isoenzymes in different tissues relates to their function in the body. 

Some enzymes exist in isozymic forms Within a single species, there may exist several different forms of enzyme catalyzing the same reaction these are known as isozymes (Markert, 1975). Generally isozymes are derived from an association of different subunits in an oligomeric enzyme with different electrophoretic mobilities. 

With few exceptions, an increase in the activity or mass of an enzyme or isoenzyme is not specific or sensitive enough to be used for identifying the type of cancer or the specific organ involvement. An exception is PSA. PSA has mild protease activity and amino acid sequence homology with serine protease of the kallikrein family.It is expressed by normal, benign, hyperplastic, and cancerous prostate glands and minimally by other tissue. Until the application of PSA as a marker for prostate cancer, tumor enzymes had lost most of their popularity for use as cancer markers. Enzymes were used historically as tumor markers before the discovery of oncofetal antigens and the advent of monoclonal antibodies. The abnormalities of enzymes as a marker for cancer are either the expression of the fetal form of the enzyme (isozyme) or the ectopic production of enzymes. 

Multiple Forms of Enzymes. Isozymes, or isoenzymes, provide an avenue for varying regulation of the same reaction at distinct locations or times. Isozymes are homologous enzymes within a single organism that catalyze the same reaction but differ slightly in structure and more obviously... 

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). 

Reaction (7) is catalyzed by starch synthases (EC 2.4.1.21 ADP-Glc 1,4-a-D-glucan 4-a-glucosyltransferase), the same reaction as the one catalyzed by the bacterial glycogen synthase (Reaction (2)). Here a different reaction number is given to stress that the final products of starch, amylose, and amylopectin, are different in structure. Isozymic forms of plant starch synthases z.i i-is,65-69 of branching enzymes 4-i 6,65,66,70-76 reported. 

Lipoprotein lipase, like many enzymes, has several isozymic forms that differ from one tissue to the next. Insulin is known to enhance lipoprotein lipase synthesis in the capillary endotheliiun next to adipocytes, whereas it has no such effect in the myocardium. Why might this have come about ... 

Adenyl Cyclase. Adenyl cyclase seems to be ubiquitous and has been found in bacteria, higher plants, and mammals. It is particulate, and therefore, must be attached to the membranes of the endoplasmic reticulum, the mitochondria, or the plasma membrane. At least in some cases, like the fat cell, adenyl cyclase has been shown to be located in the plasma membrane. The enzyme has been postulated to exist in various isozymic forms. However, the evidence for this is unconvincing, and it is generally accepted that when different hormones exert their effects on a cell by raising the levels of cAMP, they do so by activation of the same cyclase. 

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