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

The cytoplasmic isozyme of aspartate transaminase is inactivated by trypsin due to loss of a 19-residue peptide from the NH2-terminal region. A second peptide bond at Arg-25 is then cleaved by trypsin leaving a residual core protein, transaminase 26-412. Inactivation by trypsin resembles that for the mitochondrial enzyme (Sandmeier, E., and Christen, P. (1980) J. Biol. Chem. 255, 10284-10289), yet occurs 10 times faster for the cytoplasmic isozyme. In the mitochondrial enzyme, trypsin cleavage produces equal concentrations of proteins missing the first 26 and 31 amino acids. Sequence variation in the NH2-terminal regions can explain such differences. Specifically, the mitochondrial NH2 terminus has no trypsin-susceptible residue at position 19 and is stabilized by an electrostatic interaction between Asp-15 and Arg-292, whereas position 15 is a valyl residue in the cytoplasmic enzyme. Calorimetric data reveal both a decreased transition temperature (Td) and enthalpy (delta Hd) of denaturation in transaminases 20-412 and 26-412. Interaction of substrates with the active site chromophore and differential scanning calorimetry (DSC) reveal that catalytically inactive transaminases 20-412 and 26-412 can bind amino acid substrates and produce spectroscopically detectable conversion of the pyridoxal to the pyridoxamine form of the protein. By contrast, substrate analogs only form enzymatic Michaelis-type complexes.
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PMID:Selective tryptic cleavage of native cytoplasmic aspartate transaminase holoenzyme. 636 6

The aim of this case control study was to investigate the clinical significance of hepatitis B virus nuclear core antigen (HBcAg) in young cirrhotic patients. Fifteen cirrhotic patients with nuclear HBcAg in the liver biopsies were included. Their clinicopathological parameters as well as the core gene sequences were compared with those of a sex- and age-matched (1 to 2) control group. The mean follow-up periods were 124 +/- 80 and 102 +/- 43 months, respectively. Expression of nuclear HBcAg in cirrhotic liver was significantly associated with higher aspartate aminotransferase levels (P = 0.001), alanine aminotransferase levels (P < 0.001), and alpha-fetoprotein levels (P = 0.002), as well as a shorter duration to develop hepatocellular carcinoma or liver decompensation (Kaplan-Meier method, P = 0.044). Sequence analysis revealed mutations on the nuclear localization signal (NLS) of core protein in five cirrhotic patients with nuclear HBcAg (Q171K in four and Q179K in one patients). Site-directed mutagenesis experiments demonstrated that both the Q171K and Q179K mutation enhanced nuclear localization of the core protein. In conclusion, expression of nuclear HBcAg in young cirrhotic patients was associated with more severe hepatitis activities as well as an unfavourable long-term outcome. Mutations on the NLS of core protein were selected in some patients with nuclear HBcAg.
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PMID:Expression of hepatitis B virus nuclear core antigen in young cirrhotic patients is associated with an unfavourable long-term outcome. 1864 34

The substitution of amino acid (aa) 70 of arginine for glutamine and/or that of aa91 of leucine for methionine in the core protein in patients infected with hepatitis C virus (HCV) genotype 1b is associated with a poor response to pegylated interferon and ribavirin. Factors influencing these substitutions were sought in 1,097 patients infected with HCV-1b who had not received antiviral treatment. HCV variants with Arg70 and Leu91 (wild-type) decreased, while those with Gln70 and/or Met91 (mutant types) increased with age (P < 0.001). Of the 1,097 patients, 464 (42.3%) were infected with the Gln70 variant and the remaining 633 patients with the Arg70 variant. The proportion of patients with the Gln70 variant increased with the severity of liver disease (P < 0.001), elevated gamma-glutamyl transpeptidase (gamma-GTP) levels (P < 0.001) and a decrease in platelet count (P = 0.008). In univariate analysis patients with hepatocellular carcinoma, elevated aspartate aminotransferase (AST > or = 58 IU/L) and gamma-GTP (> or =61 IU/L), and decreased albumin levels (<3.9 g/dl) were more frequent in the patients with the Gln70 variant than the Arg70 variant (P = 0.003, 0.005, <0.001, and 0.031, respectively). In multivariate analysis HCC (odds ratio 1.829 [95% confidence interval 1.147-2.917]) and gamma-GTP > or =61 IU/L (1.647 [1.268-2.139]) increased the risk for the Gln70 variant. In conclusion, the substitution of amino aa70 of Arg for Gln in patients infected with HCV-1b increases with age, and it is associated with severe liver disease accompanied by elevated AST and gamma-GTP levels, as well as the development of hepatocellular carcinoma.
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PMID:Influence of amino-acid polymorphism in the core protein on progression of liver disease in patients infected with hepatitis C virus genotype 1b. 1995 Feb 30