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PubMed1983

Response to light of a specific aminotransferase for delta-aminolevulinate formation in higher plants.

It is thought that the C-5 pathway is the major, possibly the sole, route for the formation of delta-aminolevulinic acid for the biosynthesis of tetrapyrroles, including chlorophylls, in higher plants; a route involving 4,5-dioxovalerate as an intermediate followed by transamination to delta-aminolevulinic acid has been supported as one of the C-5 pathways (Granick, S., and Beale, S. I. (1978) Adv. Enzymol. Relat. Areas Mol. Biol. 46, 33-203). A specific aminotransferase for L-alanine and 4,5-dioxovalerate was found in the cucumber seeds. In dark-grown cucumber seedlings, alanine:4,5-dioxovalerate aminotransferase activity in the transitional region between shoot and root was remarkably high compared with that in the cotyledons. The exposure of the dark-grown seedlings to illumination resulted in a rapid and dramatic increase in the activity only in this transitional region. In contrast, the enzyme in the cotyledons, stem, and roots did not respond to illumination. After a 27-h illumination, the enzyme activity in the transitional region was 100-fold higher than that in the cotyledons. Other aminotransferases assayed in the transitional region did not respond to illumination. Alanine:4,5-dioxovalerate aminotransferase in the transitional region was also specific for L-alanine and 4,5-dioxovalerate.

Kinetics↗

PubMed1983

Effect of short-term prednisone therapy on aminotransferase levels and hepatitis B virus markers in chronic type B hepatitis.

We have studied the effect of short-term high-dose prednisone therapy on aminotransferase levels and hepatitis B virus markers in 6 patients with chronic type B hepatitis. All showed a decrease in amino transferase levels during treatment. This was followed by a transient increase in aminotransferase levels after prednisone was discontinued. In 5 patients, there was a decrease in hepatitis B virus deoxyribonucleic acid polymerase activity at the time of postprednisone peak of aminotransferase levels. Three of them became transiently deoxyribonucleic acid polymerase negative. All the patients have remained hepatitis B e antigen-positive throughout the period of observation. We have also found transient deoxyribonucleic acid polymerase negativity unrelated to prednisone therapy in 2 patients with chronic type B hepatitis: in one during a superimposed episode of acute type A hepatitis, and in the other during a period of pronounced alanine aminotransferase elevation. We postulate that these periods of deoxyribonucleic acid polymerase negativity are due to a decreased number of hepatitis B virus-infected cells in the liver as a consequence of hepatic necrosis.

Adult↗

PubMed1983

Apoenzyme content of serum aminotransferases in relation to plasma pyridoxal-5'-phosphate concentration.

To investigate the considerable variation in stimulation of serum aminotransferase activities by pyridoxal-5'-phosphate added in vitro, we determined the pyridoxal-5'-phosphate content of plasma, using the tyrosine decarboxylase reaction together with the catalytic activities of alanine aminotransferase and aspartate aminotransferase, with and without pyridoxal-5'-phosphate supplementation, within a group of normal human individuals. We found a very significant inverse linear relationship between plasma pyridoxal-5'-phosphate concentration and stimulation of the activities of these enzymes in serum after supplementation with pyridoxal-5'-phosphate. We conclude that the degree of stimulation of the apoenzyme of the two serum aminotransferases clearly depends on the pyridoxal-5'-phosphate concentration in vivo.

Apoenzymes↗

PubMed1980

Ornithine aminotransferase in chick embryo tissues.

Ornithine aminotransferase (E. C. 2.6.1.13) deficiency has been found to be associated with congenital atrophy of the choroid and retina of man. A deficiency in this enzyme could be associated in a causal fashion with atrophy, or it could be a coincidental association. To challenge the hypothesis that ornithine aminotransferase activity is required directly or indirectly for maintaining the eye in a functional state, it was of interest to determine the level of activity of this enzyme in normal eye tissue. We report here that the level of ornithine aminotransferase activity in pigment epithelium of chicken is 11 times that found in liver. The level of enzyme activity in retina is 80% of that found in liver. The level of enzyme present in embryonic pigment epithelium is essentially unchanged between the eighth and eighteenth day of incubation. These observations suggest strongly that ornithine aminotransferase activity is involved in maintaining the structure or function of the eye.

Animals↗

PubMed1993

[The effect of acute poisoning of rats with carbaryl on transamination reactions with participation of alpha-ketoglutarate. II. Activity of hepatic aminotransferases].

White male Wistar rats were poisoned orally with a single carbaryl dose 474 mg/kg (1/2 LD50). The activity of aminotransferases in the cytoplasma of liver homogenates catalysing the reactions between alpha-ketoglutarate and six amino acids (cysteine, lysine, phenylalanine, leucine, asparagine and valine) after 2, 4, 24 and 72 hours from the administration of the insecticide was determined. The activity of aminotransferases was expressed as the amount of glutamic acid developing during 1 hour of incubation of liver homogenate calculated for 1 g of tissue. Glutamic acid was determined spectrophotometrically after chromatographic separation on paper. The results of the investigations demonstrated that acute poisoning with carbaryl caused a statistically significant changes in the activity of two hepatic aminotransferases. A rise was observed in the activity of the enzyme causing transamination in the reaction between alpha-ketoglutarate and phenylalanine 24 hours after insecticide administration (64.1%), and a fall of the activity of the aminotransferase catalyzing the reaction between alpha-ketoglutarate and asparagine in the 4th, 24th and 72nd hours after intoxication (16.4%, 17.3% and 19.2% respectively).

Amino Acids↗

PubMed1976

Glyoxylate aminotransferase in peroxisomes from rat liver and kidney.

An aminotransferase was isolated from peroxisomes that had been separated by isopycnic centrifugation of homogenates from rat liver or kidney. The enzyme was located only in the peroxisomes and in the soluble fraction, presumably from broken peroxisomes. Within the peroxisomes, this aminotransferase was in the soluble matrix. This specific aminotransferase was not found in spinach leaves. The enzyme was relatively specific for glyoxylate as the amino group acceptor. L-Leucine and L-phenylalanine were the preferred amino donors; other amino acids were less efficiently utilized. Rates were 181 nmol X min-1 of peroxisomal protein with leucine, and 134 with phenylalanine. The rate with serine was only 28% as fast and there was no reaction with glutamate. The reactions were essentially irreversible. Treatment of peroxisomes with 0.04% Triton X-100 increased enzyme activity 80%. The enzyme in the peroxisomes was stable at 50 degrees. The enzyme was purified 100-fold. Activities with leucine, phenylalanine, and histidine could not be separated by gel filtration and DEAE-cellulose chromatography. Its molecular weight was estimated to be 72,000. Reaction kinetics were ping-pong. The Km (glyoxylate) was 0.5 mM with leucine and 0.67 mM with phenylalanine. Km (leucine) was 2.5 mM and Km (phenylalanine) was 2.8 mM. Substrate inhibition occurred at over 4 mM glyoxylate but did not occur with the amino donors. pH optima were 8.5 for leucine and phenylalanine and 6.2 for histidine. There was no requirement for exogenous pyridoxal phosphate, but activity was inhibited by phenylhydrazine and isonicotinic acid hydrazide. The glyoxylate aminotransferase developed postnatally and increased with age until rats were 40 days old. There was more activity in female than male rats. About 50% of the activity disappeared if rats were starved overnight. Clofibrate treatment of male rats increased this enzyme activity in isolated peroxisomes. Rats on a high casein diet had slightly higher enzyme activity.

Animals↗

PubMed1998

Diagnosis of trypanosomiasis in experimental mice and field-infected camels by detection of antibody to trypanosome tyrosine aminotransferase.

Sera from animals with acute and chronic Trypansoma evansi infections were examined directly for trypanosome tyrosine aminotransferase activity and indirectly for their ability to inhibit tyrosine aminotransferase activity. It was shown that sera from acutely infected mice and camels with high parasitemias contained significant levels of trypanosome tyrosine aminotransferase activity. In contrast, the sera from chronically infected mice and camels did not contain significant tyrosine aminotransferase activity, but they were able to neutralize the enzyme activity in trypanosome homogenates. The sera from camels with other pathological conditions did not neutralize this enzyme activity. It is suggested that the inhibitory factor in the chronic sera is antibody. The potential use of the direct enzyme assay and the indirect neutralization assay as diagnostic tools are discussed. Finally, the use of these assays to distinguish between early (acute) and late (chronic) infections are also suggested.

Animals↗

PubMed2002

Racial and ethnic differences in alcohol-associated aspartate aminotransferase and gamma-glutamyltransferase elevation.

BACKGROUND: Recent analyses have confirmed that Hispanic and black non-Hispanic Americans are at an increased risk for death from liver cirrhosis. The reasons for this are unknown. As a common cause of cirrhosis, differing sensitivities to alcohol-related hepatocellular injury may play a role. This study compared racial and ethnic aspartate aminotransferase and gamma-glutamyltransferase level elevations within alcohol-drinking categories. METHODS: A cross-sectional analysis of adult subjects from the Third National Health and Nutrition Examination Survey. Logistic regression models were used to estimate the risk for elevation of aspartate aminotransferase and gamma-glutamyltransferase levels among Mexican American and black non-Hispanic subjects compared with white non-Hispanic subjects within categories of alcohol use. Adjustment was made for age, sex, exposure to hepatitis C and B, and body mass index. RESULTS: Among current drinkers, black non-Hispanic and Mexican Americans were more likely to have a 2-fold elevation in aspartate aminotransferase levels when compared with white non-Hispanic Americans. This was most pronounced in the highest-frequency drinkers (Mexican Americans: odds ratio, 9.1 [95% confidence interval, 3.9-21.0]; and black non-Hispanic Americans: odds ratio, 3.1 [95% confidence interval, 1.4-6.8]). No racial and ethnic differences were apparent among current abstainers. A similar pattern was found for 2-fold gamma-glutamyltransferase level elevations. CONCLUSIONS: Among current drinkers, Mexican and black non-Hispanic Americans may have an increased risk for hepatocellular injury. These results require confirmation in other study populations for whom validated measures of quantity and pattern of drinking exist.

Adult↗

PubMed1985

Aspartate aminotransferase-like immunoreactivity in the guinea pig and monkey retinas.

The excitatory amino acids, aspartate and glutamate, have been proposed as retinal neurotransmitters. Aspartate aminotransferase (AAT) is an enzyme which is involved in the routine metabolism of these amino acids and may be involved in the specific synthesis of glutamate and/or aspartate for use as a neurotransmitter. On the basis of the hypothesis that increased levels of aspartate aminotransferase may reflect a transmitter role for aspartate and/or glutamate, we have localized aspartate aminotransferase in the guinea pig and cynamolgus monkey retinas with light and electron microscopic immunohistochemical techniques. AAT-like immunoreactivity is localized to the cones of guinea pig retina and to monkey rods. Both species contain a subpopulation of immunoreactive amacrine cells as well as a subpopulation of immunoreactive cells in the ganglion cell layer. Immunostaining is seen in bipolar cells and terminals in the monkey but not in the guinea pig retina. We have performed quantitative analysis of the immunoreactive staining in the outer plexiform layer and described the synaptic organization of immunoreactive processes in the inner plexiform layer (IPL). Labeled amacrine processes in both species form synaptic contacts predominantly to and from bipolar terminals in the inner third of the IPL and to and from other amacrine and small unidentified processes in the outer portion of the IPL. The majority of labeled bipolar terminals in the monkey retina are seen in the inner third of the IPL where they synapse exclusively onto amacrine processes. Labeled bipolar terminals in the outer third of the IPL occasionally synapse onto ganglion processes.

Animals↗

PubMed1997

Are elevated aminotransferases and decreased bilirubin additional characteristics of the metabolic syndrome?

Abnormal liver tests, as well as morphological changes in the liver, are frequent among obese patients. Other frequent disturbances are visceral fat accumulation, insulin resistance, non-insulin-dependent diabetes mellitus (NIDDM), hypertriglyceridemia, and hypertension; these are set of aberrations known as the metabolic syndrome. In order to investigate a possible relationship between the metabolic syndrome and impaired liver status we examined associations between liver tests, metabolic variables (insulin, glucose, and triglycerids), body composition and nutrition in 1,083 men (BMI 28.8-63.8 kg/m2) and 1,367 women (BMI 26.7-68.0 kg/m2) in the ongoing intervention study of Swedish Obese Subjects (SOS). Standard biochemical techniques were used to assess liver status and metabolic variables. Lean body mass (LBM) and masses of visceral and subcutaneous adipose tissue (AT) were estimated by means of computed tomography (CT) calibrated anthropometric equations. In both genders aspartate aminotransferase and alanine aminotransferase were, or tended to be, positively correlated to fasting serum insulin, visceral AT (women), and alcohol intake. In women, the aminotransferases were also correlated with fasting blood glucose. In both genders alkaline phosphatase was, or tended to be, positively associated with visceral AT, insulin (women), and glucose. Bilirubin was negatively correlated to insulin and visceral AT in men and women. Additional multivariate analyses indicated that alcohol had less explanatory power than serum insulin for the examined liver tests, especially among women. These results suggest that pathological liver tests in the obese may represent an expression of the metabolic syndrome.

Adipose Tissue↗

PubMed2005

In vivo carbon-13 magnetization transfer effect. Detection of aspartate aminotransferase reaction.

One of the most remarkable achievements of in vivo NMR spectroscopy has been the detection of rapid enzyme-catalyzed exchange reactions using phosphorus-31 magnetic resonance spectroscopy-based magnetization transfer experiments. In this paper, we report, for the first time, the in vivo carbon magnetization transfer (CMT) effect and in vivo detection of the CMT effects of the alpha-ketoglutarate <--> glutamate and the oxaloacetate <--> aspartate reactions, both of which are catalyzed by aspartate aminotransferase. By saturating the carbonyl carbon of alpha-ketoglutarate at 206 ppm in alpha-chloralose anesthetized adult rat brain, the unidirectional glutamate --> alpha-ketoglutarate flux was determined to be 78 +/- 9 mumol/g/min (mean +/- SD, n = 11) following i.v. infusion of [1,6-(13)C(2)]D-glucose. Contribution from aspartate aminotransferase-catalyzed partial reactions to the observed CMT effects was emphasized. Because of the large chemical shift separation between the alpha-carbons of the amino acids and the carbonyl carbons of the corresponding cognate keto acids, the spillover of the saturation radiofrequency pulses to the alpha-carbon resonances was negligible. The results indicate that the magnetization transfer effects of aspartate aminotransferase-catalyzed reactions can be used as new biomarkers accessible to non-invasive in vivo magnetic resonance spectroscopy techniques.

Animals↗

PubMed1994

The N-terminal region of mature mitochondrial aspartate aminotransferase can direct cytosolic dihydrofolate reductase into mitochondria in vitro.

Two fused genes were constructed which encode for two chimeric proteins in which either 10 or 191 N-terminal amino acids of mature mitochondrial aspartate aminotransferase had been attached to the entire polypeptide chain of cytosolic dihydrofolate reductase. The precursor and mature form of mitochondrial aspartate aminotransferase, dihydrofolate reductase and both chimeric proteins were synthesized in vitro and their import into isolated mitochondria was studied. Both chimeric proteins were taken up by isolated organelles, where they became protease resistant, thus indicating the ability of the N-terminal portion of the mature moiety of the precursor of mitochondrial aspartate aminotransferase to direct cytosolic dihydrofolate reductase into mitochondria.

Aspartate Aminotransferases↗

PubMed1995

Use of protease sensitivity to probe the conformations of newly synthesised mutant forms of mitochondrial aspartate aminotransferase.

Sensitivity to digestion with pronase has been used to show that the precursor form of mitochondrial aspartate aminotransferase, the form lacking the N-terminal presequence, that with a deletion of the first 9 residues and mutants of the mature enzyme in which residue Cys-166 is mutated to alanine or serine, all retain unfolded conformations after synthesis in a reticulocyte lysate. In the presence of lysed mitochondria the various forms of mitochondrial aspartate aminotransferase retained their susceptibilities to pronase in a way that mirrored the efficiencies with which they are imported into intact mitochondria. The results are interpreted as showing that the presequence of mitochondrial aspartate aminotransferase is not uniquely required for interaction with cytosolic factors required to maintain the newly synthesised protein in a form competent for interacting with, and being imported into, mitochondria.

Alanine↗

PubMed1994

Structure of genes that encode isozymes of aspartate aminotransferase in Panicum miliaceum L., a C4 plant.

The cytosolic and mitochondrial isozymes of aspartate aminotransferase (AspAT) function in the C4 photosynthetic cycle in NAD-malic enzyme-type C4 plants and are expressed at high levels in mesophyll cells and bundle sheath cells, respectively. We constructed a genomic library from Panicum miliaceum, a NAD-malic enzyme-type C4 plant, and cloned the genes for these isozymes. The sequence of the cloned gene for cytosolic AspAT spans 7800 bp and consists of 12 exons. The sequence of the cloned gene for mitochondrial AspAT spans 9000 bp and consists of 10 exons. The results of primer-extension analysis suggest that transcription may be initiated from multiple adjacent sites. Both genes have significant GC-rich regions around the site of initiation of transcription, and these regions showed no CpG suppression. The 5'- flanking regions of both genes include several short sequences similar to the regulatory elements found in other genes for components of the photosynthetic machinery. In particular, the cytosolic AspAT gene contains sequences similar to nuclear protein-binding sites in other mesophyll-expressed C4 photosynthetic genes and the mitochondrial AspAT gene contains elements for light-sensitive and constitutive expression of a bundle sheath-expressed gene. The results of Southern analysis indicated that there are at least two genes that encode each isozyme in the genome of P. miliaceum. A comparison of intron-insertion positions between AspAT genes of plants and animals revealed that several introns are located at identical positions. On the basis of a phylogenetic tree among AspATs and tyrosine aminotransferase, we have shown that the introns of aminotransferase genes antedate the divergence of eubacteria, archaebacteria, and eukaryotes.

Animals↗

PubMed1987

Localization of glutamate, glutaminase, aspartate and aspartate aminotransferase in the rat midbrain periaqueductal gray.

Glutamate and aspartate are putative excitatory neurotransmitters in the central nervous system. The present study utilized novel monoclonal antibodies against fixative-modified glutamate and aspartate and polyclonal antisera against the amino acid synthesizing enzymes, glutaminase and aspartate aminotransferase, to analyze the distribution of these amino acids in the rodent midbrain periaqueductal gray. Glutamate-, aspartate-, glutaminase- and aspartate aminotransferase-like immunoreactive neurons, fibers and processes are present throughout the rostrocaudal length of the periaqueductal gray. Glutamate- and glutaminase-like immunoreactive neurons displayed a similar homogeneous pattern of distribution, being localized predominantly to the lateral and dorsal subdivisions of the periaqueductal gray. Co-localization experiments suggest that glutamate and glutaminase are in fact co-contained within the same PAG neurons. Aspartate aminotransferase-like immunoreactive neurons were distributed in a pattern similar to glutamate and glutaminase with the exception that fewer cells were stained in the dorsocaudal and the rostral third of the PAG. Aspartate-like immunoreactive neurons were less numerous than glutamate-like immunoreactive cells and were located in the lateral aspect of the PAG. These results demonstrate a specific and distinct distribution of glutamate and aspartate immunoreactive neurons and support recent data suggesting that glutamate and aspartate serve as excitatory neurotransmitters in the PAG.

Animals↗

PubMed1991

The in vitro-synthesized precursor and mature mitochondrial aspartate aminotransferase share the same import pathway in isolated mitochondria.

Both the precursor and the mature form of mitochondrial aspartate aminotransferase were synthesized in a cell-free coupled transcription/translation system directed by the recombinant expression plasmid pOTS-pmAspAT and pOTS-mAspAT, respectively. Both newly synthesized forms of the protein were imported into isolated mitochondria, with the precursor correctly processed to the mature form. In both cases the import process showed resistance to externally added pronase and was abolished in mitochondria treated with the uncoupler carbonyl cyanide m-chlorophenylhydrazone. Moreover the imported products showed the same intramitochondrial localization as judged by a subfractionation procedure. In both cases import was time dependent and was completed in about 15 min. Finally a competitive inhibition of the import of the precursor of aspartate aminotransferase was found due to externally added purified aspartate aminotransferase.

Animals↗

PubMed1992

Import of mutant forms of mitochondrial aspartate aminotransferase into isolated mitochondria.

To gain some insight into the role played by certain protein domains in the import of mitochondrial aspartate aminotransferase in isolated mitochondria, three protein mutants were constructed by using the plasmid pOTS-mAspAT, which contains the nucleotide sequence encoding for the mature form of this enzyme. Two mutant proteins in which Cys-166 was substituted with either serine or alanine and another protein lacking the nine N-terminal amino acids were all synthesized in a cell-free transcription/translation system. Comparison was made among the newly synthesized mutant proteins and the newly synthesized wild type aspartate aminotransferase with respect to their capability to enter mitochondria. All the mutant proteins proved to be able to enter mitochondria even though with a lower efficiency than the wild type enzyme. Interestingly the thiol reagent mersalyl proved to inhibit import of both wild type enzyme and serine mutant, whereas import of alanine mutant was found to be insensitive to mersalyl, thus showing that Cys-166 is the unique -SH group involved in import. Import of mitochondrial aspartate aminotransferase by mitochondria is shown to involve certain protein domains present in the mature protein, two of them being the Cys-166 and the N-terminal regions.

Amino Acid Sequence↗

PubMed1990

Certain N-terminal peptides inhibit uptake of mature aspartate aminotransferase by isolated mitochondria.

To gain insight into the uptake of mature aspartate aminotransferase by isolated mitochondria, the capability of certain cyanogen bromide peptides from mature beef heart mitochondrial aspartate aminotransferase to inhibit enzyme uptake was kinetically tested. N-terminal peptides (1-9 and 10-31) proved to inhibit the rate of aspartate aminotransferase uptake respectively in purely competitive and non-competitive ways, whereas other peptides distal from the N-terminus (203-217, 321-327 and 328-353) were found to be completely ineffective.

Amino Acid Sequence↗