Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is the most abundant mutagenic heterocyclic amine in cooked foods. Two mouse tumor cell lines, BMT11 and FM3A, were exposed to its proximate form, 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine (N-OH-PhIP). Fifty-six subclones of BMT11 and 39 subclones of FM3A were isolated and analyzed by DNA fingerprinting. Treatment with 10-20 microM N-OH-PhIP gave rise to extra bands or shifted bands, but treatment without N-OH-PhIP did not. This suggests that mutations resulting from recombination were induced. The mutation frequencies were 21-53% and 22-35% for BMT11 and FM3A, respectively. These findings suggest that PhIP induces recombinational mutations.
Mol Carcinog 1994 Feb
PMID:2-Hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine induction of recombinational mutations in mammalian cell lines as detected by DNA fingerprinting. 814 10

2-Amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) are two members of a family of carcinogenic heterocyclic amines (HAs) found in cooked meats that form DNA adducts after activation to N-acetoxy derivatives. The ability of IQ- and PhIP-DNA adducts to inhibit gene expression was investigated using a human growth hormone (hGH) reporter gene in a pUC12-based mammalian expression vector under the control of either the herpes simplex virus-1 thymidine kinase promoter or the human immunodeficiency virus-1 long terminal repeat. The plasmids were treated in vitro with 0, 5, 10, or 40 microM N-hydroxy-IQ or N-hydroxy-PhIP in the presence of a 10-fold molar excess of acetic anhydride to generate the N-acetoxy derivatives in situ. The adduct levels in the plasmids were quantitated by the 32P-postlabeling method. The adducted (and control) plasmids were each transfected into repair-deficient or -proficient Chinese hamster ovary cells, and expression of hGH was measured by immunoassay of growth hormone secreted into the cell medium. The results showed that IQ- and PhIP-DNA adducts inhibited gene expression in both plasmids and that the degree of inhibition of hGH production was proportional to the levels of IQ- and PhIP-DNA adducts. The degree of inhibition, however, was independent of the promoter, despite the differences in the strengths of the two promoters to drive hGH production. Repair capacity influenced the extent of inhibition of gene expression by HA adducts since, in general, fewer adducts were needed to inhibit reporter gene expression in repair-deficient cells than in repair-proficient cells. In both cell lines, DNA adducts of PhIP appeared to be more potent in inhibiting hGH expression than adducts of IQ. Whether alteration of gene expression by HA adducts plays a role in the carcinogenicity of these compounds deserves further study.
Mol Carcinog 1994 May
PMID:Inhibition of plasmid reporter gene expression in CHO cells by DNA adducts of 2-amino-3-methylimidazo[4,5-f]quinoline and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine. 818 27

Three crystal structures of wild type E. coli aspartate aminotransferase (E.C.2.6.1.1) in space group P2(1) have been determined at resolution limits between 2.6 and 2.35 A. The unliganded enzyme and its complexes with the substrate analogues maleate and 2-methylaspartate resulted in different conformations. The unit cell parameters of the unliganded and the inhibited enzyme are a = 87.2, b = 79.9, c = 89.8 A and beta = 119.1 degrees, and a = 85.4, b = 79.8, c = 89.5 A and beta = 118.6 degrees, respectively. The crystallographic symmetry is pseudo-C222(1). The liganded enzyme structures were solved by difference Fourier techniques from that of a Val39-->Leu mutant partially refined to an R-factor of 0.22 at 2.85 A. They have a "closed" conformation like the chicken mAATase:maleate complex. The models were refined to R-factors of 0.19 (maleate complex) and 0.18 (2-methylaspartate complex) by molecular dynamics and restrained least squares methods. The unliganded crystal form was solved by molecular replacement and refined to an R-factor of 0.19 at 2.5 A resolution. The structure is in a "half-open" conformation, with the small domain rotated about 6 degrees from the closed conformation. The cofactor pyridoxal phosphate has a more relaxed conformation than in mAATase. Both maleate and 2-methylaspartate are hydrogen-bonded to the active site as in mAATase. The C alpha-CH3 bond of 2-methylaspartate is oriented at right angles to the cofactor pyridine ring, the most productive orientation for alpha-deprotonation of the substrate L-aspartate. Comparisons with earlier determined eAATase structures in space group C222(1) revealed differences that can probably be attributed to the somewhat lower resolution of the orthorhombic structures and/or mutations in the eAATases used in those studies. The present P2(1) structures confirm the justification of extrapolating properties of active site point mutants to the vertebrate isozymes. They will serve as reference in the interpretation of the properties of further site-directed mutants in continued studies of structure-function relationships of this enzyme.
J Mol Biol 1994 Jun 03
PMID:Crystal structures of Escherichia coli aspartate aminotransferase in two conformations. Comparison of an unliganded open and two liganded closed forms. 819 59

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine is a potent mutagenic agent produced during thermal processing of meats. Since 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine has a similar structure to tetrahydroisoquinoline, a mitochondria toxic compound, we determined whether or not this compound shows detrimental effects on mitochondrial electron transport activities in various rat tissues. Administration of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, 100 mg/kg twice a week for 4 weeks, decreased significantly the activity of complex I in mitochondrial electron transport chain of heart, diaphragm, and psoas major, while it did not affect the activities of complex I in the liver mitochondria. Concerning the activities of complexes II, III, and IV, no significant effects were observed irrespective of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine administration. Age-related deterioration of mitochondrial function seems to be a major contributor to age-related decline in cellular function. From our results, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine might act as an accelerator of age-related decline in mitochondrial function.
Biochem Mol Biol Int 1993 Aug
PMID:Detrimental effects of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, a mutagenic agent, on mitochondrial respiration among various rat tissues. 822 Feb 32

Asp222 of aspartate aminotransferase is an active-site residue which interacts with the pyridine nitrogen of the coenzyme, pyridoxal 5'-phosphate (PLP). The roles of Asp222 in the catalytic mechanism of Escherichia coli aspartate aminotransferase have previously been explored by site-directed mutagenesis. These studies confirmed that a negatively charged residue at position 222 is essential for catalysis, but the reason for this remained speculative. In the present studies, the roles of Asp222 were clarified experimentally by analyzing the mutant D222A enzyme (Asp222 replaced by Ala) reconstituted with the coenzyme analog N(1)-methylated PLP (N-MePLP). Spectroscopic and kinetic analyses showed that Asp222 stabilizes the protonated N(1) of PLP, raising the pKa value of N(1) by more than five units, in the active site of AspAT. The positive charge at N(1) accelerates abstraction of the alpha-proton from the amino acid substrate, stabilizing the transition state by 1.4 to 4.5 kcal.mol-1 in the reaction with aspartate. X-ray crystallographic (2.0 A resolution) and CD spectroscopic studies suggest that the coenzyme analog is not held in a proper orientation within the active site of D222A (N-MePLP). This may account for the finding that the catalytic activity was recovered only partially by the reconstitution of D222A with N-MePLP. These results fully support the following postulated role of Asp222: the negative charge of Asp222 stabilizes the positive charge at N(1) of PLP and thereby enhances the function of PLP as an electron sink.
J Mol Biol 1993 Dec 20
PMID:Role of an active site residue analyzed by combination of mutagenesis and coenzyme analog. 826 22

The enzyme 3 beta-hydroxysteroid dehydrogenase isomerase (3 beta-HSD/I) is an essential step in the biosynthesis of steroid such as progesterone, mineralo- and gluco-corticoids, estrogens and androgens in steroidogenic tissues. It is considered to be mainly localized in microsomes; however, 3 beta-HSD/I activity has also been described to be associated with mitochondrial preparations. In this study, we examined the subcellular distribution of 3 beta-HSD/I in bovine adrenocortical tissue and we characterized the catalytic properties of the enzyme present in the various cell compartments. About 30% of the total 3 beta-HSD/I activity was found to remain tightly associated with the purified mitochondrial pellet. The 3 beta-HSD/I and 3-ketoreductase activities were found in microsomes as well as in mitochondria. The 3 beta-HSD/I associated with the mitochondrial fraction did not require addition of exogenous NAD+. When the pyridine nucleotide was reduced following addition of substrates of the tricarboxylic acids cycle, the mitochondrial 3 beta-HSD/I activity decreased, suggesting that the enzyme utilizes NAD+ available from the matrix space. By contrast, the microsomal enzyme was inactive in the absence of exogenous NAD+. Submitochondrial fractionation disclosed that 3 beta-HSD/I was associated (i) with the inner membrane and (ii) with a particulate fraction sedimenting in a density gradient between inner and outer membranes. This fraction was characterized as contact sites between the two membranes. 3 beta-HSD/I specific activity was much higher in this fraction than in the inner mitochondrial membrane. Altogether, these observations suggest that these mitochondrial intermembrane contact sites may represent a special organization of functional significance, facilitating both the access of cholesterol to the inner membrane where cytochrome P-450scc is located and the rapid transformation of its product, pregnenolone, to progesterone, through 3 beta-HSD/I activity.
J Steroid Biochem Mol Biol 1993 Dec
PMID:Dual subcellular localization of the 3 beta-hydroxysteroid dehydrogenase isomerase: characterization of the mitochondrial enzyme in the bovine adrenal cortex. 827 11

Heterocyclic amines present in cooked foods are known to produce colon tumors in F344 rats at a high incidence, indicating the possibility of involvement of ras gene activation in colon carcinogenesis in rats as in humans. We examined mutations at codons 12, 13, and 61 of the Ki-ras, Ha-ras, and N-ras genes by polymerase chain reaction--direct sequencing in seven colon tumors in F344 rats induced by 2-amino-6-methyldipyrido-[1,2-a:3',2'-d]imidazole (Glu-P-1), 11 induced by 2-amino-3-methylimidazo[4,5-f]quinoline, and nine induced by 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine. A Ki-ras gene mutation (G-->T at the second position in codon 12) was found in one Glu-P-1-induced colon adenocarcinoma. None of the other 26 tumors had mutations in any of these three ras family genes. These results indicate that in rats, colon carcinogenesis induced by heterocyclic amines may be induced by alterations of other oncogenes or tumor suppressor genes. We think this experimental system using carcinogens to which humans are exposed is a good model for studying alterations of other genes in human colon tumors in which no Ki-ras alterations are observed.
Mol Carcinog 1993
PMID:Rare frequency of activation of the Ki-ras gene in rat colon tumors induced by heterocyclic amines: possible alternative mechanisms of human colon carcinogenesis. 835 90

The basic (pKa = 8.49) 1,4-dihydropyridine B 874-67 [[3-(C1R,2S)- 2-methylamino-1-phenylpropyl]-5-methyl-1,4-dihydro-2,6-dimethyl-(4R)-4-( 3-nitrophenyl)pyridine-3,5-dicarboxylate hydrochloride] has unique properties; it can discriminate two populations of alpha 1 subunits in 1,4-dihydropyridine-sensitive calcium channels labeled with the neutral 1,4-dihydropyridine (+)-[3H]PN 200-110. The two populations, which occur in proportions of approximately 2:1 in rabbit skeletal muscle membranes and highly purified calcium channel preparations, differ approximately 20-fold in their affinity. The corresponding diastereomer, B 874-66, and other 1,4-dihydropyridines (neutral, basic, or permanently charged) do not share this property. The two populations were observed at 2 degrees, 22 degrees, and 37 degrees in similar proportions. Heterogeneity was also observed for guinea pig heart membrane calcium channels labeled with (+)-[3H]PN 200-110. Heterotropic allosteric regulators, Ca2+, and Mg2+, but not Ba2+ and Ni2+, abolished the discriminatory activity of B 874-67 at 2 degrees and 22 degrees, regardless of whether binding of the neutral 1,4-dihydropyridine was stimulated or inhibited. It is proposed that the two alpha 1 subunit populations differ with respect to their 1,4-dihydropyridine binding domain. The structural basis for the two populations is unclear but may relate to the functional heterogeneity of membrane-bound and highly purified calcium channel preparations previously observed by others.
Mol Pharmacol 1993 Feb
PMID:Heterogeneity of L-type calcium channel alpha 1 subunits: stereoselective discrimination of different populations by the novel 1,4-dihydropyridine B 874-67. 838 14

Coupled to the N-methyl-D-aspartate (NMDA) receptor-channel complex is a strychnine-insensitive binding site for glycine. Pharmacological antagonism of glycine binding at this site can produce anticonvulsant activity. Derivatives of the glycine antagonists kynurenic acid and 2-carboxy-indole were synthesized and evaluated for anticonvulsant effects. Compounds were tested in mice against seizures induced by electroshock and pentylenetetrazole, and in the rotorod assay for neurological deficit. The derivatives were also assayed for binding at the NMDA-associated glycine site. The most potent anticonvulsant was ethyl 4-methylamino-5,7-dichloro-2-quinoline carboxylate. This compound provided protection against maximal electroshock (MES) induced seizures at a dose level including 5-fluoro-2-indole carboxylic acid and the diethyl ester of 2,6-pyridine dicarboxylic acid.
Mol Chem Neuropathol 1993 Aug
PMID:Anticonvulsant activity of antagonists for the NMDA-associated glycine binding site. 839 87

Lipophosphoglycan-like glycoconjugates were isolated, purified and partially characterized from Tritrichomonas foetus and Trichomonas vaginalis. Cell surface radiolabeling of both trichomonads by the galactose oxidase/NaB[3H]4 technique indicated that the glycoconjugate was located on the cell surface of the parasites. The glycoconjugates were extracted from the delipidated residue fraction with the solvent, water/ethanol/diethylether/pyridine/NH4OH (15:15:5:1:0.017) and were purified to homogeneity by Sepharose CL-4B followed by octyl-Sepharose chromatography and methanol precipitation. The glycoconjugates migrated as broad bands upon SDS-PAGE. The T. foetus glycoconjugate contained large amounts of fucose along with some mannose, galactose, glucosamine and glucose and trace amounts of galactosamine and inositol. The T. vaginalis glycoconjugate appeared to contain large amounts of glucosamine and galactose along with some glucose, mannose and traces of galactosamine and inositol. The surface-labeled glycoconjugates from both parasites was found to be deaminated with nitrous acid and susceptible to phosphatidylinositol-specific phospholipase C, indicating the presence of a phospholipid anchor. Furthermore, these glycoconjugate were found to contain phosphate and were labile to hydrolysis by mild acid, strongly suggesting that the intact molecule is related to Leishmania lipophosphoglycans (LPG). The most striking and the unique features of these glycoconjugate molecules are the presence of large amounts of fucose in T. foetus and glucosamine in T. vaginalis along with the presence of galactosamine in both parasites. These results indicate that these glycoconjugates are new types of LPG-like molecules expressed on the trichomonad cell surface and are structurally distinct from Leishmania LPG.
Mol Biochem Parasitol 1993 Feb
PMID:Lipophosphoglycan-like glycoconjugate of Tritrichomonas foetus and Trichomonas vaginalis. 843 19


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