Ornithine-5-aminotransferase

Ornithine aminotransferase (OAT) is a mitochondrial matrix enzyme that catalyzes the primary reaction 

However, following its formation, the semialdehyde undergoes a spontaneous cyclization and is converted to a A -pyrroline-5-carboxylic acid (P5C), a proline precursor. 

The homogenate was prepared from the liver of an adult female rat in 20% sucrose containing potassium phosphate (pH 7.4). The homogenate was centrifuged at 1000 rpm for 15 minutes and stored at —20°C. 

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This enzyme catalyzes the reaction of an w-amino acid with pyruvate to produce L-alanine and an aldehyde-containing carboxyhc acid. See Lysine 6-Aminotransferase Ornithine Aminotransferase... 

ORNITHINE TRANSCARBAMOYLASE d-ORNITHINE 4,5-AMINOMUTASE ORNITHINE AMINOTRANSFERASE ORNITHINE DECARBOXYLASE Ornithine carbamoyltransferase,... 

ORNITHINE TRANSCARBAMOYLASE Ornithine ketoacid aminotransferase, ORNITHINE AMINOTRANSFERASE Ornithine oxo-acid aminotransferase, ORNITHINE AMINOTRANSFERASE ORNITHINE TRANSCARBAMOYLASE Orotate,... 

KYNURENINE AMINOTRANSFERASE LEUCINE AMINOTRANSFERASE LYSINE 2,3-AMINOMUTASE LYSINE 6-AMINOTRANSFERASE LYSINE DECARBOXYLASE METHIONINE y-LYASE ORNITHINE AMINOTRANSFERASE PHENYLALANINE DECARBOXYLASE PHOSPHATIDYLSERINE DECARBOXYLASE... 

Fig. 1.3 Reactions showing synthesis of glutamate in brain. Aspartate aminotransferase (1) glu-taminase (2) glutamate dehydrogenase (3) GABA aminotransferase (4) alanine aminotransferase (5) ornithine aminotransferase (6) Al-pyrroline 5-carboxylic acid dehydrogenase (7) and asparagine synthetase (8)...

It has been noted in the case of several enzymes that their artificial prococious induction is reversible in that, unless the injection of the appropriate hormone is repeated, the enzyme disappears again. Why is it then that after its natural appearance at the scheduled time, the persistence of the enzyme does not hinge on the continued action of that hormone For example, glucocorticoid is undoubtedly the essential developmental stimulus for the hepatic ornithine aminotransferase(14), a member of the late suckling cluster. Its normal emergence on day 12 can be prevented by prior adrenalectomy, its precocious synthesis (5-10 days before schedule) can be evoked by an injection of cortisol, and yet no loss at all is incurred by adrenalectomy performed at or after the time at which ornithine aminotransferase has attained near adult or adult values (i.e. on day 20 or later). 

A question of stability. Pyridoxal phosphate (PLP) is a coenzyme for the enzyme ornithine aminotransferase. The enzyme was purified from cells grovm in PLP-deficient media as well as from cells grown in media that contained pyridoxal phosphate. The stability of the enzyme was then measured by incubating the enzyme at 37°C and assaying for the amount of enzyme activity remaining. The following results were obtained. 

Gyrate atrophy of the retina 258870 Ornithine aminotransferase <1 100,000 Myopia, night blindness, progressive loss of peripheral vision ... 

The urea so formed is distributed throughout the body water and excreted. The renal clearance of urea is less than the glomerular filtration rate because of passive tubular back-diffusion. Diffusion of urea in the intestine leads to formation of ammonia, which enters the portal blood and is converted to urea in liver. Reentry of ornithine into mitochondria initiates the next revolution of the urea cycle. Ornithine can be converted to glutamate-y-semialdehyde (which is in equilibrium with its cyclic form A -pyrroline-5-carboxylate) by ornithine aminotransferase and de-carboxylated to putrescine by ornithine decarboxylase. Ornithine is also produced in the arginine-glycine trans-amidinase reaction. 

Decarboxylation of ornithine to putrescine by ornithine decarboxylase serves as a source of the polyamines spermidine and spermine. Ornithinemia results from deficiency of ornithine aminotransferase or ornithine... 

Metabolism of proline (1) A -pyrroline-5-carboxylate (P5C) synthase (2) ornithine aminotransferase (3) P5C reductase (4) proline oxidase (5) P5C dehydrogenase (6) ornithine decarboxylase. 

Point mutation affecting processing of the ornithine aminotransferase precursor protein in gyrate atrophy. J Biol Chem 264 17432-17436. 

McClatchey AI, Kaufman DL, Berson EL, Tobin AJ, Shih VE, et al. 1990. Splicing defect at the ornithine aminotransferase (OAT) locus in gyrate atrophy. Am J Hum Genet 47 790-794. 

O Donnell JJ, Vannas Sulonen K, Shows TB, Cox DR. 1988. Gyrate atrophy of the choroid and retina Assignment of the ornithine aminotransferase structural gene to human chromosome 10 and mouse chromosome 7. Am J Hum Genet 43 922-928,... 

Ramesh V, McClatchey Al, Ramesh N, Benoit LA, Berson EL, et al. 1988. Molecular basis of ornithine aminotransferase deficiency in B-6-responsive and-nonresponsive forms of gyrate atrophy. Proc Natl Acad Sci USA 85 5777-5780. 

Kasahara M, Matsuzawa T, Kokubo M, Gushiken Y, Tashiro K, Koide T, Watanabe H, Katunuma N (1986) Immunohistochemical localization of ornithine aminotransferase in normal rat tissues by Fab -horseradish peroxidase conjugates. J Histochem Cytochem 34 1385-1388. 

Ornithine aminotransferase Acetylornithine aminotr. Succinylornithine aminotr. Ala-glyoxylate aminotransferase... 

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