Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P17174 (aspartate aminotransferase)
 14,872 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The enhanced stability usually exhibited by enzymes after immobilization may be attributed either to a stabilization effect of the solid matrix on the bound enzyme molecule or to the influences of diffusional limitations on the observed activity. To allow the comparison of the intrinsic statilities of free and bound enzymes a simple graphical procedure for the removal of external diffusional effects of stability curves is described. It is based on the determination of substrate concentration differences between the enzyme micro- and macroenvironment. Application of the method to aspartate aminotransferase bound to collagen membranes indicates that diffusional limitations for oxaloacetate are partly responsible for the observed stability enhancement. Comparison of the graphically obtained intrinsic profile with the stability curve of the soluble enzyme further demonstrate that the binding itself greatly increases the stability of aspartate aminotransferase.
 ...
PMID:Comparison of intrinsic stabilities of free and bound enzymes by graphical removal of diffusional effects. 91 65

The kinetic properties of aspartate aminotransferase covalently bound to collagen are compared to those of the free enzyme. In the bound state, the enzyme exhibits a greater affinity for glutamate, but a lower affinity for oxalacetate. In order to assess precisely the contribution of diffusional limitations on the heterogeneous enzyme kinetics, a simple modeling of diffusional effects on a two-substrate enzymatic reaction is developed. According to this quantitative analysis, diffusional limitations for oxalacetate alone account for the increased and decreased enzyme affinities toward its two substrates. Consequently, coupling of the enzyme to collagen does not significantly affect its intrinsic kinetic properties.
 ...
PMID:Kinetics of soluble and collagen-bound aspartate aminotransferase: diffusional effects with a two-substrate enzymatic reaction. 91 49

Two new methods of activation were developed to graft enzymes on collegen films. They involved chemical modifications of surface groups of collagen either by Woodward's reagent "K" or by EDC, a water-soluble derivative of carbodiimide. EDC was a better coupling agent and a detailed study was conducted with this agent. It could be used either in a global method of activation and coupling, or in a two-step procedure of activation of collagen, followed by spontaneous coupling of enzyme. All enzymes tested were successfully bound: malate dehydrogenase, lactate dehydrogenase, aspartate aminotransferase, urease, creatine kinase, hexokinase. The influence on the yield of grafted enzyme, of pretreatment of films, time and temperature of EDC activation, concentration of EDC and enzyme, protecting agents was studied. Stability of enzyme activity on storage was greatly increased after grafting. A co-grafted dual system creatine kinase/heoxkinase, was achieved which exhibited a good efficiency. A striking renaturing process at 0-4degreesC after thermal denaturation, was observed with hexokinase.
 ...
PMID:Grafting of enzymes on collagen films using Woodward's reagent "K" and a water-soluble carbodiimide derivative. 95 53

A study was conducted to investigate morphologic as well as metabolic characteristics of microcarrier-attached hepatocytes in culture, and also to evaluate the effect of intraperitoneal transplantation of the microcarrier-attached hepatocytes on acute hepatic failure in rats induced by D-galactosamine (GalN). Rat hepatocytes were isolated by collagenase perfusion, and cultured on collagen-coated microcarriers. Protein synthesis estimated by [14C] leucine incorporation was four-fold higher in microcarrier culture than in cell suspension. The rates of albumin, transthyretin and bile acid syntheses in hepatocytes cultured on microcarriers were similar to those in monolayer culture. When microcarrier-attached hepatocytes were intraperitoneally transplanted into rats with Galn-induced acute liver failure, a marked improvement in survival rate was observed as compared with control rats which received injections of microcarriers alone (80% vs 0% beyond 6 days of transplantation). Mean serum glutamate oxaloacetate transaminase (SGOT), serum glutamate pyruvate transaminase (SGPT), methionine and glucose levels were similar in both groups, while serum bilirubin and ammonia levels were lower (P less than 0.1, P less than 0.05) in rats transplanted with the microcarrier-attached hepatocytes. Immunohistochemical examinations revealed that the transplanted hepatocytes around microcarriers had albumin synthesis activity, whereas almost no albumin synthesis was demonstrated in recipient liver. In conclusion, intraperitoneal transplantation of the microcarrier-attached hepatocytes will provide sufficient metabolic support, representing detoxication of ammonia (and presumably bilirubin) and synthesis of albumin, to allow GalN-damaged liver function to restore. Microcarrier culture of isolated hepatocytes seems to be one of the most appropriate tools for an artificial liver support.
 ...
PMID:Effects of intraperitoneal transplantation of microcarrier-attached hepatocytes on D-galactosamine-induced acute liver failure in rats. 168 85

We used electron microscopy (EM) to analyze 52 biopsy samples from 22 patients who were receiving long-term weekly oral doses of methotrexate (MTX) for the treatment of rheumatoid arthritis. Forty-eight biopsy samples were obtained after 2-6 years of continuous treatment, and 4 samples were obtained before treatment was begun. Specimens were graded for neutral fat, secondary and tertiary lysosomes, and smooth endoplasmic reticulum (SER) in hepatocytes, and for collagen in the perisinusoidal space (Disse's space). We examined the correlations between the EM findings and the light microscopic (LM) findings in the same biopsy specimens, and between the EM findings and the results of simultaneous monthly measures of aspartate transaminase, alkaline phosphatase, bilirubin, and albumin levels, as well as history of alcohol consumption before MTX treatment and monthly assessments of clinical status during the course of treatment. The presence of collagen was minimally increased in these sequential biopsy samples, whereas fat, lysosomes, and SER were decreased. The SER decrease was statistically significant. EM findings of collagen in the space of Disse did not correlate with early fibrotic changes observed with LM. Thus, after as long as 6 years of weekly oral treatment with MTX, hepatic ultrastructural changes are minimal and are not clinically significant. The use of EM for sequential biopsy studies allows the quantitation of long-term hepatic changes that may be more limited than the impression gained after LM analysis.
 ...
PMID:Electron microscopic analysis of sequential liver biopsy samples from patients with rheumatoid arthritis. Correlation with light microscopic findings. 280 23

Previous studies have pointed towards a cofactor role for pyridoxal 5'-phosphate (PLP) in lysyl oxidase, the enzyme that generates the peptidyl aldehyde precursor to the lysine-derived cross-linkages in elastin and collagen. The nature of a carbonyl moiety in purified bovine aortic lysyl oxidase was explored in the present study. A PLP dinitrophenylhydrazone could not be isolated from lysyl oxidase, although corresponding preparations of aspartate aminotransferase, a PLP-dependent enzyme, yielded this derivative, as revealed by h.p.l.c. Analysis of lysyl oxidase for PLP after reduction of the enzyme by NaBH4, a procedure that converts PLP-protein aldimines into stable 5'-phosphopyridoxyl functions, also proved negative in tests using monoclonal antibody specific for this epitope. Lysyl oxidase was competitively inhibited by phenylhydrazine, and inhibition became irreversible with time at 37 degrees C, displaying a first-order inactivation rate constant of 0.4 min-1 and KI of 1 microM. [14C]Phenylhydrazine was covalently incorporated into the enzyme in a manner that was prevented by prior modification of the enzyme with beta-aminopropionitrile, a specific active-site inhibitor, and which correlated with functional active-site content. The chemical stability of the enzyme-bound phenylhydrazine exceeded that expected of linkages between PLP and proteins. The absorption spectrum of the phenylhydrazine derivative of lysyl oxidase was clearly distinct from that of the phenylhydrazone of PLP. It is concluded that lysyl oxidase contains a carbonyl cofactor that is not identical with PLP and that is bound to the enzyme by a stable chemical bond.
 ...
PMID:Reactivity of a functional carbonyl moiety in bovine aortic lysyl oxidase. Evidence against pyridoxal 5'-phosphate. 287 97

We evaluated the concept that the vascular entrance of both bacterial and nonbacterial particulate material could lead to hepatic parenchymal cell injury, either due to postphagocytic Kupffer cell activity or the margination of activated leukocytes in the liver. Injection of denatured, collagen-coated particles as well as heat-killed bacteria were used as particulate challenges. Hepatic parenchymal cell injury in vivo during postoperative sepsis was evaluated by plasma aspartate aminotransferase (AST) and ornithine carbamyl transferase (OCT) enzyme levels over 3-72 h. AST and OCT levels elevated following either laparotomy plus cecal ligation (mild sepsis) or laparotomy plus cecal ligation with puncture (severe sepsis), with the peak level at 24 h. In addition, the direct intravenous injection of either nonbacterial foreign particles or heat-killed Pseudomonas aeruginosa into normal rats also produced a dose-dependent elevation of AST and OCT. The plasma level of either AST or OCT actually increased 350-400% after injection of the non-bacterial particles. A similar dose related elevation in enzymes followed the intravenous injection of heat-killed Pseudomonas. To differentiate the potential contribution of activated hepatic Kupffer cells versus activated marginated neutrophils to the in vivo hepatic injury, we determined the release of the hepatic specific enzyme OCT by cultured hepatic parenchymal cells when they were exposed to isolated Kupffer cells or isolated PMNs that were activated by exposure to dead bacteria. Bacteria alone when added to cultured hepatocytes did not induce significant OCT release. In contrast, activated PMNs but not Kupffer cells induced a significant (p less than 0.05) release of OCT from parenchymal cells into the culture media. Thus, in vivo transient hepatic parenchymal cell injury with post-operative sepsis may be mediated by the margination of activated PMNs in the liver.
 ...
PMID:Hepatocyte injury during post-operative sepsis: activated neutrophils as potential mediators. 342 80

Malate dehydrogenase (EC 1.1.1.37) and aspartate aminotransferase (EC 2.6.1.1) are present in porcine blood platelets in both mitochondria and the cytosol. The latter enzyme is inhibited in a typical way by aminooxycompounds and cycloserine. Blocking of aminotransferase or inhibition of the mitochondrial dicarboxylate carrier by butylmalonate stimulates lactate production by intact platelets and inhibits their aggregation induced by ADP or collagen. These results indicate that the reoxidation of cytosolic NADH via the malate-aspartate shuttle is important for covering the energy demand of platelets necessary for their stimulation.
 ...
PMID:Importance of the malate-aspartate shuttle for the reoxidation of glycolytically produced NADH and for cell aggregation in porcine blood platelets. 368 99

In bovine platelets aspartate aminotransferase has a high activity. The enzyme in vitro is inhibited in a dose dependent manner by aminooxyacetate (IC50 = 10(-4) M), hydroxylamine (IC50 = 10(-4) M), and cycloserine (IC50 = 5 X 10(-3). The inhibitory effect of all the three compounds is strongest at low substrate (aspartate) concentration. Blocking of aspartate aminotransferase activity by these compounds in intact platelets is accompanied by the inhibition of ADP and collagen-induced aggregation. Among the three compounds the strongest inhibitor of platelet aggregation was hydroxylamine, which was also the most effective inhibitor of aspartate aminotransferase. Other metabolic blockers, i.e. dinitrophenol (DNP), rotenone and antimycin also inhibited the aggregation of platelets, and a synergism has been demonstrated between DNP, rotenone and antimycin A action on platelet aggregation and blockade of aspartate aminotransferase activity. The results are interpreted to mean that transamination is of importance in the energy production in the activated platelet, probably through its participation in reducing equivalents transport from the cytosol to the mitosol via the malate: oxaloacetate: aspartate shuttle.
 ...
PMID:The importance of aspartate aminotransferase for platelet aggregation. 375 38

To study the effect of facilitated diffusion of the intermediate metabolite, oxaloacetate, on the coupled reaction of aspartate aminotransferase (L-aspartate: 2-oxoglutarate aminotransferase, EC 2.6.1.1) and malate dehydrogenase (L-malate:NAD+ oxidoreductase, EC 1.1.1.37), these enzymes were co-immobilized on the surface of a collagen film. The kinetic properties of the immobilized enzymes were compared with those observed with the enzymes in solution. Since the reactions correspond to the cytosolic enzymes, they have been studied in the direction aspartate aminotransferase toward malate dehydrogenase. Coupled enzymes in solution showed classical behaviour. A lag-time was observed before they reached a steady state and this lag-time was dependent on the kinetic properties of the second enzyme, malate dehydrogenase. The same lag-time was observed when malate dehydrogenase in solution was coupled with aspartate aminotransferase bound to the film. When aspartate aminotransferase in solution was coupled with malate dehydrogenase bound to the collagen film, a very long lag-time was observed. Theoretical considerations showed that in the latter case, the lag-time was dependent on the kinetic properties of the second enzyme and the transport coefficient of the intermediate substrate through the boundary layer near the surface of the film. Then both enzymes were co-immobilized on the collagen film. The coupled activity of aspartate aminotransferase and malate dehydrogenase was compared for films with an activity ratio of 5 and 0.8. In both cases, a highly efficient coupling was observed. In the former case, where malate dehydrogenase was rate-limiting, 81% of this limiting activity was observed. In the latter case, aspartate aminotransferase was rate-limiting and 82% of its rate was obtained for the final product formation. The linear increase of product formation with time corresponded fairly well to the theoretical equations developed in the paper. To interpret these rate equations, one should assume that the intermediate substrate oxaloacetate formed by aspartate aminotransferase was used by malate dehydrogenase in the diffusion layer near the film, before diffusing in the bulk solution.
 ...
PMID:Coupled reaction of immobilized aspartate aminotransferase and malate dehydrogenase. A plausible model for the cellular behaviour of these enzymes. 399 45


1 2 3 4 5 6 7 8 9 10 Next >>