Aminotransferases isoenzymes

P. Christen, R. Jaussi, N. Juretic, P.K. Mehta, T.I. Hale, and M. Ziak. 1990. Evolutionary and biosynthetic aspects of aspartate aminotransferase isoenzymes and other aminotransferases N. Y. Acad. Sci. 585 331-338. (PubMed)... 

DeRosa, C., and Swiefc, R. W- (1975). Metabolic implications of the distribution of the alanine aminotransferase isoenzymes. /. Biol. Chem. 2S0, 7961-7967. 

Rej R, Keese CR, Giaever I. Direct immunochemical determination of aspartate aminotransferase isoenzymes, Clin Chem 1981 27 1597-601. 

Figure 21-3 The ratio (mean SD) of mitochondrial to total AST in hepatic diseases.The difference between alcoholic hepatitis and other hepatic diseases is statistically significant (p < 0.05). (Modified from Panteghini A1, FalseW f Chiari , MalchiodiA, Determination of aspartate aminotransferase isoenzymes in hepatic diseases. Lab j Res Lab Med 1983 i 0 515-9.)...

Panteghini M. Aspartate aminotransferase isoenzymes. Clin Biochem 1990 23 311-9. 

Recasens M, Delaunoy JP (1981) Immunological properties and immunocytochemical localization of cysteine sulfinate or aspartate aminotransferase-isoenzymes in rat CNS. Brain Res 205 351-361. 

Ruscak, M., J. Orlicky, and V. Zubor. 1982. Isoelectric focusing of the alanine aminotransferase isoenzymes from the brain, liver and kidney. Comparative Biochemistry and Physiology 1... 

Gel electrophoresis evidence suggested that different aspartate aminotransferase isoenzymes were present in chloroplasts and mitochondria from spinach leaves. In addition, two electrophoretically distinct forms of aspartate aminotransferase were seen in the peroxisomal fraction (Yamazaki and Tolbert, 1970). Kanamori and Matsumoto (1974) found two isoenzymes of glutamate oxaloacetate aminotransferase in roots of rice seedlings, whereas there were three isoenzymes in the shoots. However, in the roots, where the soluble and mitochondrial enzymes both consisted of multiple forms, the electrophoretic pattern was similar for both, i.e., the electrophoretic forms were not organelle specific. Other workers concluded that extensively purified mitochondrial and soluble alanine aminotransferases in tomato fruits were the same protein (Gazeu-Reyjal and Crouzet, 1976) and that there were not organelle-specific isoenzymes. 

Isoenzyme patterns for transaminase enzymes other than aspartate aminotransferase have been less well studied, but there is evidence for mesophyll and bundle sheath specific forms of alanine aminotransferase in mesophyll and bundle sheath cells (Hatch, 1973) and also evidence for a plastid alanine aminotransferase isoenzyme (Thomas and Stoddart, 1974). 

Until now it has not been elucidated what is the origin of mitochondrial sulphurtransferases, although majority of mitochondrial proteins is synthesized on cytoplasmic ribosomes and later transferred to the organelle /for references see Schatz and Mason, 197 / Recently Marra and co-workers /1978/ studied selective permeation of labelled aspartate aminotransferase isoenzymes into mitochondria in vitro. Following their ideas.we labelled crystalline bovine liver rhodanese with and Incubated it with fresh preparation of... 

Enzymes, measured in clinical laboratories, for which kits are available include y-glutamyl transferase (GGT), alanine transferase [9000-86-6] (ALT), aldolase, a-amylase [9000-90-2] aspartate aminotransferase [9000-97-9], creatine kinase and its isoenzymes, galactose-l-phosphate uridyl transferase, Hpase, malate dehydrogenase [9001 -64-3], 5 -nucleotidase, phosphohexose isomerase, and pymvate kinase [9001-59-6]. One example is the measurement of aspartate aminotransferase, where the reaction is followed by monitoring the loss of NADH ... 

Antithyroid drags have several side effects. The most frequent side effects are maculopapular rashes, pruritus, urticaria, fever, arthralgia and swelling of the joints. They occur in 1-5% of patients [1, 2]. Loss of scalp hair, gastrointestinal problems, elevations of bone isoenzyme of alkaline phosphatase and abnormalities of taste and smell are less common. The incidence of all these untoward reactions is similar with MMI and PTU. Side effects of MMI are dose-related, whereas those of PTU are less clearly related to dose [1]. PTU may cause slight transient increases of serum aminotransferase and y-glutamyl transpeptidase concentrations but also severe hq atotoxicity whereas methimazole or carbimazole can be associated with cholestasis. The side... 

In the malate shuttle (left)—which operates in the heart, liver, and kidneys, for example-oxaloacetic acid is reduced to malate by malate dehydrogenase (MDH, [2a]) with the help of NADH+HT In antiport for 2-oxogluta-rate, malate is transferred to the matrix, where the mitochondrial isoenzyme for MDH [2b] regenerates oxaloacetic acid and NADH+HT The latter is reoxidized by complex I of the respiratory chain, while oxaloacetic acid, for which a transporter is not available in the inner membrane, is first transaminated to aspartate by aspartate aminotransferase (AST, [3a]). Aspartate leaves the matrix again, and in the cytoplasm once again supplies oxalo-acetate for step [2a] and glutamate for return transport into the matrix [3b]. On balance, only NADH+H"" is moved from the cytoplasm into the matrix ATP is not needed for this. 

Many enzymes exist within a cell as two or more isoenzymes, enzymes that catalyze the same chemical reaction and have similar substrate specificities. They are not isomers but are distinctly different proteins which are usually encoded by different genes.22 23 An example is provided by aspartate aminotransferase (Fig. 2-6) which occurs in eukaryotes as a pair of cytosolic and mitochondrial isoenzymes with different amino acid sequences and different isoelectric points. Although these isoenzymes share less than 50% sequence identity, their internal structures are nearly identical.24-27 The two isoenzymes, which also share structural homology with that of E. coli,28 may have evolved separately in the cytosol and mitochondria, respectively, from an ancient common precursor. Tire differences between them are concentrated on the external surface and may be important to as yet unknown interactions with other protein molecules. 

Transaminases participate in metabolism of most of the amino acids, over 60 different enzymes have been identified.142163 Best studied are the aspartate aminotransferases, a pair of cytosolic and mitochondrial isoenzymes which can be isolated readily from animal hearts. Their presence in heart muscle and brain in high concentration is thought to be a result of their functioning in the malate-aspartate shuttle... 

Several markers should no longer be used to evaluate cardiac disease, including aspartate aminotransferase, total CK, total lactate dehydrogenase (LDH), and LDH isoenzymes. Due to their wide tissue distribution, these markers have poor specificity for the detection of cardiac injury. Because total CK and CK-MB have served as standards for so many years, some laboratories may continue to measure them to allow for comparisons to cardiac troponin over time, before discontinuing use of CK and CK-MB. In addition, the use of total CK in developing countries may be the preferred or only alternative for financial reasons. However, it should be clear that, for monitoring ACS patients to assist in clinical classification, cardiac troponin is the preferred biomarker. 

Both aspartate aminotransferase and alanine aminotransferase are released into the blood after damage to tissues or after cell death. Consequently, they are used as diagnostic tools when heart or liver damage has occurred, such as after a heart attack or in hepatitis, respectively. Other enzymes are also released into the blood at such times. For example, damage to heart muscle is further characterized by the presence of isoenzymes of creatine kinase or lactate dehydrogenase in the plasma. 

Lactate dehydrogenase (human isoenzyme) Prostatic acid phosphatase (hmnan prostate) Alanine aminotransferase (pig heart) r a-Amylase (human pancreas)... 

Product inhibition is a cause of nonlinearity of reaction progress curves during fixed-time methods of enzyme assay. For example, oxaloacetate produced by the action of aspartate aminotransferase inhibits the enzyme, particularly the mitochondrial isoenzyme. The inhibitory product may be removed as it is formed by a coupled enzymatic reaction malate dehydrogenase converts the oxaloacetate to malate and at the same time oxidizes NADH to NADL... 

The liver can be involved in CF. Biliary cirrhosis secondary to bile duct obstruction occurs in as many as 18% of patients, whereas fatty infiltration occurs in about 30% of patients in a pattern unrelated to nutritional status. Bile ducts may be obstructed by inspissated mucus, which may lead to focal or multilobar cirrhosis. Such hepatic involvement can occur at any age but is more common with advancing age and can lead to portal hypertension, esophageal varices, and hypersplenism. The most common laboratory abnormality associated with hepatic involvement is elevated serum hepatic isoenzymes (gamma-glutamyltranspeptidase, alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase)." ... 

Immunological methods for enzymes, more specifically isoenzymes, such as lactate dehydrogenase-1 (167, 168), mitochondrial aspartate aminotransferase (169), prostatic acid phosphatase (170, 171,172), and creatine kinase-MB (173, 174, 175), have been in use in the clinical laboratory for 10 years. However, the use of the immunological rather than catalytic properties of enzymes has not provided the opportunities for standardization that was anticipated a number of years ago (176, 177, 178). It is only within the last year that a working group on CK-MB mass assay was formed under the auspices of the Standards Committee of the American Association for Clinical Chemistry (AACC). The objective of this working group is to prepare a reference material to calibrate methods that are based on the principle of CK-MB mass measurement. 

The enzyme catalyzing the reversible transamination of alanine and a-ketoglutarate is alanine aminotransferase (ALT), and isoenzymes occur in both the cytosol and mitochondria. This enzyme occurs in many tissues and is particularly active in the liver. An increase of this enzyme in the serum (sometimes referred to as SGPT, serum glutamic pyruvic transaminase) is indicative of hepatic damage. 

Many examples of aminotransferase activity have been described in helminths, although the enzymes have rarely been characterized (1,17). Most are specific for a-ketoglutarate as the amino acceptor but have broad specificity with respect to the amino donor. There is considerable variation in the potential amino acid donors from one species to another. Those aminotransferases that have been characterized show some similarities to rat liver enzymes. As in protozoa, alanine aminotransferase is ubiquitous and, together with asparate aminotransferase, is usually the most active member of this group. Isoenzymes of alanine aminotransferase have been found in both cytoplasm and mitochondria. The results of a survey of nematode alanine aminotransferases suggest that there is a greater overall capacity for the synthesis of alanine than for its catabolism, the opposite of the situation with the rat liver enzymes (17). 

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