Transaminase distribution

Glutamic acid dehydrogenase is widely distributed in microorganisms and higher plants as a catalyst in the synthesis of L-glutamic acid from a-ketoglutaric acid and free ammonia. Transaminase is contained in a wide variety of microorganisms. 

Daly, E. C. Aprison, M. H. (1974). Distribution of serine hydroxymethyltransferase and glycine transaminase in several areas of the central nervous system of the rat. J. Neurochem. 22, 877-85. 

Transaminases The transaminases catalyze the reversible transformation of a-ketoacids into amino acids. Most frequently, the 2 transaminases GPT (= glutamic pyruvic transaminase) (or ALT = alamine transaminase) and GOT (= glutamic oxaloacetic transaminase) (or AST = aspartate transaminase) are used for enzyme diagnostics (F. DeRitis et at., 1955 F. Wroblewski et al., 1955). (s. tab. 5.4) While GOT is distributed evenly, the GPT concentration continuously decreases from periportal to pericentral in the acinus. These are considered to be the basic parameters in the diagnosis and follow-up of hepatocellular disease. If the cause of elevated transaminases remains unclear, the indication for liver biopsy is given. (28, 30, 31, 34)... 

Ribavirin This guanosine analogue was first used experimentally by o. Reichard et al. (1991) and in chronic hepatitis C by J. Andersson et al. (1991). It is rapidly absorbed and distributed in the body, but is excreted slowly (half-life 79 hours). The bioavailability is 45-65%. As a monotherapy, it only leads to a decrease in transaminases and a slight improvement in histological activity. Ribavirin may not exhibit a direct antiviral effect, but can trigger a favourable response to interferon. When combined with IFN, ribavirin proved far more efficacious in chronic hepatitis C (immunomo-dulation ) without any increase in the typical side effects of IFN. (49, 51, 53) (s. p. 707)... 

Transaminases are widely distributed throughout the body. AST is found primarily in the heart, liver, skeletal muscle, and Iddney, whereas ALT is found primarily in the liver and kidney, with lesser amounts in heart and skeletal muscle (Table 21-2). ALT is exclusively cytoplasmic both mitochondrial and cytoplasmic forms of AST are found in cells. These are genetically distinct isoenzymes with a dimeric structure composed of two identical polypeptide subunits of about 400 amino acid residues. 

Transamination reactions combine reversible amina-tion and deamination, and they mediate redistribution of amino groups among amino acids. Transaminases (aminotransferases) are widely distributed in human tissues and are particularly active in heart muscle, liver, skeletal muscle, and kidney. The general reaction of transamination is... 

Often there is no good clinical test available to determine the exact type of hepatic lesion, short of liver biopsy. There are certain patterns of enzyme elevation that have been identified and can be helpful (Table 38-3). ° The specificity of any serum enzyme depends on the distribution of that enzyme in the body. Alkaline phosphatase is found in the bile duct epithelium, bone, and intestinal and kidney cells. 5-Nucleotidase is more specific for hepatic disease than alkaline phosphatase, because most of the body s store of 5 -nucleotidase is in the liver. Glutamate dehydrogenase is a good indicator of centrolobular necrosis because it is found primarily in centrolobular mitochondria. Most hepatic cells have extremely high concentrations of transaminases. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) are commonly measured. Because of their high concentrations and easy liberation from the hepato-cyte cytoplasm, AST and ALT are very sensitive indicators of necrotic lesions within the liver. After an acute hepatic lesion is established, it may take weeks for these concentrations to return to normal. ... 

Fonnum, F. (1968) The distribution of glutamate decarboxylase and aspartate transaminase in subcellular fractions of rat and guinea-pig brain. Biochem. J., 106,401-412. 

The metabolic steps in gluconeogenesis occur in two intracellular compartments (Fig. 3.2) the cytosol and the mitochondrial matrix. The enzymes of the tricarboxylic acid cycle reside in the mitochondrial matrix, apart from succinate dehydrogenase which is present in the inner mitochondrial membrane, whereas most of the enzymes of the gluconeogenic pathway are present in the cytosol. Transaminases, such as alanine aminotransferase and aspartate aminotransferase, are present both in mitochondria and cytosol of the domestic fowl liver (Sarkar, 1977). One of the control enzymes in gluconeogenesis, PEPCK, has a different intracellular distribution in avian liver compared with mammalian liver (Table 3.3). PEPCK in both pigeon and domestic fowl liver is present almost exclusively (> 99%) in mitochondria (Soling et al.. 1973), whereas in most mammals that have been studied, it is present mainly in the cytosol, and only present, if at all, in smaller amounts in... 

Lin C T, Li H Z, and Wu J,-Y (1983b) Immunocytochemical studies and comparison of regional distribution of L-glutamate decarboxylase, gamma aminobutync acid transaminase, cysteinsul-finic acid decarboxylase, aspartate aminotransferase and somatostatin m rat retina Brain Res, 270, 273-283... 

Transaminases are widely distributed in microorganisms, plant, and animal tissues (see reviews ). The type reaction catalyzed is the following ... 

A comparative quantitative assay of the rates of transamination of different amino acids in the different animal tissues using improved assay methods has not been reported. Unpublished studies from the author s laboratory reveal that the pattern of transaminase activity for different amino acids varies quantitatively as well as qualitatively. This difference also applies to the intracellular distribution of transminases. Glutamic-... 

It appears from studies to date that the glutamic-oxalacetic transaminase is the most active and widely distributed of all the transaminases in all cells studied.As a generalization it would appear that the reaction... 

Other. The most active and the most widely distributed transaminase is the glutamic-oxaloacetic enzyme ... 

Enzymes which catalyze the transfer of an amino group from an amino acid to a keto acid (or aldehyde) without the intermediate formation of free ammonia are called transaminases (or aminophorases). These enzyme systems, first described by Braunstein and Kritzmann (878), are widely distributed in plants, microorganisms, and animal tissues (see reviews, 879-881). 

The role of the coupled transaminase-glutamic dehydrogenase stems in amino acid nthesis has been discussed in Section IV, C. The possible role of L-amino acid oxidase in amino add syntheds has recently been proposed by Radhakrishnan and Meister ). However, the same objections raised above in relation to the low activity of this enzyme and its limited distribution must be answered before the role of this enzyme in amino acid biosyntheds can be conddered. 

There is a decrease in the plasma concentration of vitamin Bg with increasing age, and some studies have shown a high prevalence of abnormal transaminase activation coefficient in elderly subjects, suggesting that the elderly may be at risk of vitamin Bg deficiency. It is not known whether this reflects an inadequate intake, a greater requirement, or changes in the tissue distribution and metabolism of the vitamin with increasing age. 

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