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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Heart sarcolemma has been shown to possess three catalytic sites (I, II and III) for methyl transferase activity (Panagia V, Ganguly PK and Dhalla NS. Biochim Biophys Acta 792:245-253, 1984). In this study we examined the effect of phosphatidylethanolamine N-methylation on ATP-independent Ca2+ binding and ATPase activities in isolated rat heart sarcolemma. Both low affinity (1.25 mM Ca2+) and high affinity (50 microM Ca2+) Ca2+ binding activities were decreased following incubation of sarcolemmal membranes with AdoMet under optimal conditions for site II and III. Similarly, Ca2+ ATPase activities measured at 1.25 mM and 4 mM Ca2+ were depressed by phospholipid N-methylation. S-adenosyl homocysteine, a specific inhibitor of phospholipid N-methylation, prevented the depression of low affinity Ca2+ binding and Ca2+ ATPase activities, whereas the methylation-induced effect on the high affinity Ca2+ binding was not influenced by this agent. Pretreatment of sarcolemma with methyl acetimidate hydrochloride, an amino group blocking agent, also prevented the methylation-induced inhibition of both Ca2+ binding and Ca2+ ATPase. A further decrease in Ca2+ binding and Ca2+ ATPase activities together with a marked increase in the intramembranal level of PC was seen when membranes were methylated under the site III conditions in the presence of phosphatidyldimethylethanolamine as exogenous substrate. There was no effect of phospholipid methylation on sarcolemmal Na+-K+ ATPase and Mg2+ ATPase activities. These results indicate a role of phospholipid N-methylation in the regulation of sarcolemmal Ca2+ ATPase and low affinity ATP-independent Ca2+ binding.
Mol Cell Biochem 1987 Nov
PMID:Decreased Ca2+-binding and Ca2+-ATPase activities in heart sarcolemma upon phospholipid methylation. 284 56

The inactivation of elongation factor 2 (EF-2) by diphtheria toxin requires the presence of a post-translationally modified histidine residue in EF-2. This residue, diphthamide, has the structure 2-[3-carboxyamido-3-(trimethylammonio)propyl]histidine. The present work was undertaken to study the pathway of diphthamide biosynthesis using diphtheria toxin-resistant yeast mutants (Chen. J.-Y., Bodley, J. W., and Livingston, D. M. (1985) Mol. Cell. Biol. 5, 3357-3360) which are defective in diphthamide formation. We demonstrate here that one of these mutants (dph5) contains a toxin-resistant form of EF-2 which can be converted in vitro to a toxin-sensitive form through the action of an enzyme present in other yeast strains. Both this toxin-resistant EF-2 and its modifying enzyme have been partially purified and evidence is presented that the modifying enzyme is a specific S-adenosylmethionine:EF-2 methyltransferase. In vitro complementation to diphtheria toxin sensitivity required S-adenosylmethionine, and when partially purified components were incubated with [methyl-3H]S-adenosylmethionine, label was incorporated specifically into EF-2. Hydrolysis of labeled EF-2 yielded diphthine (the unamidated form of diphthamide) and a single chromatographically separable labeling intermediate. We conclude that the S-adenosylmethionine:EF-2 methyltransferase adds at least the last two of the three methyl groups present in diphthine and that this modification is sufficient to create diphtheria toxin sensitivity. Evidence is also presented for the existence of an ATP-dependent amidating enzyme which catalyzes the final step in the biosynthesis of diphthamide in EF-2.
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PMID:Biosynthesis of diphthamide in Saccharomyces cerevisiae. Partial purification and characterization of a specific S-adenosylmethionine:elongation factor 2 methyltransferase. 304 77

The gene expression of nine phages of the T7 group was compared after infection of Escherichia coli B(P1). With the exception of phage 13a which grew normally, all of them infected E. coli B(P1) abortively. Differences were found in the efficiency of host killing which ranged from 100% for phage 13a to 37% for phage A1122. Infection by T7 prevented colony formation by about 70% of the cells but they showed filamentous growth until about 2 h after infection. It was shown by SDS-polyacrylamide gel electrophoresis and autoradiography of [35S]methionine-labelled phage-coded proteins that all phages except for 13a showed measurable expression only of the early genes. No correlation was observed between killing capacity and the pattern of gene expression, and the ability to hydrolyse S-adenosyl-methionine (SAM, a cofactor for the P1 restriction endonuclease) by means of a phage-coded SAMase. Mixed infection of E. coli B(P1) with 13a and T7 yielded mixed progeny indistinguishable from that observed after mixed infection of the normal host E. coli B. Genetic crosses with amber mutants of 13a and T7 showed that the 13a marker opo+ (overcomes P one), required for growth on B(P1), is located in the early region, to the left of gene 1 (RNA polymerase gene).
Mol Gen Genet 1988 Jun
PMID:Inhibition of gene expression of T7-related phages by prophage P1. 304 52

In Saccharomyces cerevisiae the SAM1 and SAM2 genes encode two distinct forms of S-adenosylmethionine (AdoMet) synthetase. In a previous study we cloned and sequenced the SAM1 gene (D. Thomas and Y. Surdin-Kerjan, J. Biol. Chem. 262:16704-16709, 1987). In this work, the SAM2 gene was isolated by functional complementation of a yeast double-mutant strain, and its identity was ascertained by gene disruption. It has been sequenced and compared with the SAM1 gene. The degree of homology found between the two genes shows that SAM1 and SAM2 are duplicated genes. Using strains disrupted in one or the other SAM gene, we have studied the regulation of their expression by measuring the steady-state level of mRNA after growth under different conditions. The results show that the expression of the two SAM genes is regulated differently, SAM2 being induced by the presence of excess methionine in the growth medium and SAM1 being repressed under the same conditions. The level of mRNA in the parental strain shows that it is not the sum of the levels found in the two disrupted strains. This raises the question of how the two AdoMet synthetases in S. cerevisiae interact to control AdoMet synthesis.
Mol Cell Biol 1988 Dec
PMID:SAM2 encodes the second methionine S-adenosyl transferase in Saccharomyces cerevisiae: physiology and regulation of both enzymes. 307 75

Studies have been performed in rats in order to test whether methionine reverses the inhibition of formate oxidation produced by nitrous oxide by virtue of the conversion of methionine to formate. At a dose of methionine (100 mg/kg, 671 mumol/kg) that completely reverses the nitrous oxide inhibition of formate oxidation no significant conversion of the methyl group, carboxyl, or backbone of methionine to formate was apparent. No increases in hepatic formate levels were seen after the administration of 671 mumol/kg methionine or ethionine, and formate treatment did not alter the rate of 14CO2 formed after methionine was administered labeled in the methyl, carboxyl, or backbone position. The reversal of nitrous oxide inhibition of formate oxidation was found to correlate temporally with either S-adenosylmethionine levels after methionine administration or S-adenosylethionine levels following ethionine treatment. After methionine or ethionine administration, elevated hepatic steady state levels of tetrahydrofolate were observed and were coincident with elevated S-adenosylmethionine or S-adenosylethionine. Since formate oxidation rates are dependent on the hepatic tetrahydrofolate level, the mechanism of methionine reversal of nitrous oxide inhibition appears to be related to effects of hepatic S-adenosylmethionine which are important in maintaining and regulating tetrahydrofolate, rather than formate generation from methionine.
Mol Pharmacol 1987 Aug
PMID:The role of formate and S-adenosylmethionine in the reversal of nitrous oxide inhibition of formate oxidation in the rat. 311 58

The effect of D,L-alpha-difluoromethylornithine (DFMO) on thiol and polyamine levels in Trypanosoma brucei was investigated by isolating trypanosomes from infected rats treated with DFMO for 12-48 h. Concentrations of thiols, polyamines and other amino-compounds were measured by an automated high-performance liquid chromatography method. The levels of DFMO in rat plasma (0.02-1.34 mM) is similar to that found in the parasites (0.27-0.99 mM), concentrations which exceed the Ki of DFMO for T. brucei ornithine decarboxylase. Treatment with DFMO increases intracellular levels of ornithine, S-adenosylmethionine and decarboxylated S-adenosylmethionine and decreases putrescine and spermidine. Putrescine is undetectable after 12 h treatment with DFMO and after 48 h spermidine is decreased by 76%. By 48 h, the spermidine-glutathione conjugates glutathionylspermidine and dihydrotrypanothione (bis(glutathionyl)spermidine) are also decreased by 41 and 66%, respectively. In contrast, levels of glutathione show a slight increase. These changes in metabolite levels are consistent with the biosynthetic pathway proposed for Crithidia fasciculata, where trypanothione is synthesized from spermidine and glutathione via the intermediates N1- and N8-glutathionyl-spermidine. Trypanothione is thought to have two important roles in trypanosomatid metabolism: the maintenance of intracellular thiols in the correct redox state and in the removal of hydrogen peroxide and other hydroperoxides. Thus, it is proposed that depletion of this metabolite may be an important contributory factor to the selective toxic effect of DFMO, particularly in its synergistic effect with other trypanocidal drugs.
Mol Biochem Parasitol 1987 Jun
PMID:In vivo effects of difluoromethylornithine on trypanothione and polyamine levels in bloodstream forms of Trypanosoma brucei. 311 34

Activities of enzymes involved in transmethylation reactions were determined in bloodstream trypomastigotes of Trypanosoma brucei brucei infection in rats. S-Adenosyl-L-methionine synthetase (EC 2.5.1.6), S-adenosyl-L-homocysteine hydrolase (EC 3.3.1.1), cystathionine synthase (EC 4.2.1.21), as well as several transmethylases were detected and localized in cytosolic rather than particulate fractions. High performance liquid chromatography analysis of methionine cycle intermediates in cells from untreated rats and from rats treated with the ornithine decarboxylase inhibitor DL-alpha-difluoromethylornithine (DFMO) indicated that the inhibitor causes pronounced changes in concentrations of these intermediates and dramatically alters the methylation index of the cell. These findings demonstrate another in the wide range of metabolite disturbances attributable to DFMO and reflect the belief that multiple biochemical events are a sequel of its action on trypanosomes.
Mol Biochem Parasitol 1988 Jan 01
PMID:Effect of DL-alpha-difluoromethylornithine on methionine cycle intermediates in Trypanosoma brucei brucei. 312 29

Growth of Trichomonas vaginalis in a semi-defined medium was inhibited by 5 mM DL-alpha-difluoromethylornithine (DFMO). Using high pressure liquid chromatography (HPLC) analysis, putrescine and cadaverine levels were found to be 90 and 100% reduced, respectively after 120 h exposure, whilst spermidine and spermine levels were unchanged. Putrescine (40 microM) and cadaverine (6 microM) were detected in the spent media from control cultures. Neither of these diamines was detected in spent media from 72 h DFMO-treated cultures. Changes in intracellular levels of amine precursors were also determined by HPLC. There was a transient increase in ornithine to 39 nmol (mg protein)-1 at 48 h in the DFMO-treated cells while it remained undetectable in control cells throughout the experiment. Arginine and citrulline levels remained high, decreasing to control levels only after 72 h. Only spermine (1 mM) rescued DFMO-treated cells, and this is discussed with respect to the presence of a putative spermine-specific oxidase designated by its sensitivity to aminoguanidine. Aerobic incubation of growing (normal) cells with [14C]spermine resulted in the production of an unknown metabolite (19% of total label), whose content was reduced to 5% under anaerobic conditions. Decarboxylated S-adenosylmethionine remained undetectable in DFMO-treated cells, and the methylation index (ratio of S-adenosylmethionine to S-adenosylhomocysteine) did not change from the control value of 9.3. Ornithine decarboxylase, S-adenosylmethionine synthetase, S-adenosylmethionine:L-homocysteine methyltransferase, and S-adenosylhomocysteine hydrolase enzyme activities were detected. However, S-adenosylmethionine decarboxylase, spermidine synthase or spermine synthase were not detected. These findings are discussed with reference to the arginine dihydrolase pathway whose end products are putrescine and ATP.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Biochem Parasitol 1988 Oct
PMID:Effect of DL-alpha-difluoromethylornithine on polyamine synthesis and interconversion in Trichomonas vaginalis grown in a semi-defined medium. 314 9

CheZ is the product of one of six genes required for sensory processing in Escherichia coli and Salmonella typhimurium chemotaxis. This 24-kDa cytoplasmic protein is modified by a posttranslational methylation reaction. The modified residue has been identified by analysis of radioactively labeled protein from two-dimensional electrophoretograms and Edman degradation of CheZ protein isolated by immunoaffinity chromatography using anti-CheZ monoclonal antibodies. The methylated group is an N-monomethylmethionine residue at the amino terminus of CheZ. L16, a ribosomal protein that is required for peptidyltransferase activity during protein synthesis, is also methylated at its amino-terminal methionine (Chen, R., Brosius, J., and Wittmann-Liebold, B. (1977) J. Mol. Biol. 111, 173-181). Homologous sequences at the amino termini of L16 and CheZ raise the possibility that a single S-adenosylmethionine-dependent methyltransferase modifies both proteins.
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PMID:A second type of protein methylation reaction in bacterial chemotaxis. 329 25

Adenosine dialdehyde (2'-O-[(R)-formyl(adenin-9-yl)methyl]-(R)-glyceraldehyde), formed by periodate oxidation of adenosine, is a potent inhibitor of S-adenosylhomocysteine hydrolase (EC 3.3.1.1.) in mouse L929 cells. Consequently, the dialdehyde produces an increase in intracellular levels of S-adenosylhomocysteine and subsequent inhibition of S-adenosylmethionine-dependent macromolecular methylations. In the present study we show that adenosine dialdehyde is also a potent inhibitor of vaccinia virus plaque formation in monolayer cultures of L cells. When added to the culture medium immediately following attachment of the virus, concentrations of the dialdehyde as low as 0.5 microM produce greater than 90% inhibition of plaque formation after 72 hr. The efficacy of the compound is greatest when added within 8 hr of virus attachment and gradually decreases in a time-dependent manner when added after this point. Treatment of L cells with 5 microM adenosine dialdehyde for 60 min prior to virus infection causes a transient, but virtually complete loss of S-adenosylhomocysteine hydrolase activity and subsequent 3-fold increase in the intracellular S-adenosylhomocysteine/S-adenosylmethionine ratio. Continuous exposure of infected cells to the dialdehyde results in prolonged inhibition of S-adenosylhomocysteine hydrolase accompanied by a 10-fold increase in the S-adenosylhomocysteine/S-adenosylmethionine ratio. Associated with these changes in the dialdehyde-treated, infected cells are an inhibition of early virus-specific protein synthesis and a 13% decrease in methylation of the cytoplasmic poly A+-mRNA. The antiviral action of this compound thus appears to be related to a decrease in viral mRNA methylation (e.g., the 5'-terminal cap structure) which results in suppressed translation of viral proteins essential for virus replication.
Mol Pharmacol 1987 May
PMID:Adenosine dialdehyde: a potent inhibitor of vaccinia virus multiplication in mouse L929 cells. 357 93


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