Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.2.1.15 (pectinase)
 2,440 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The transfer of a methyl group from S-adenosyl-L-methionine onto the carboxyl group of alpha-1,4-linked-galactosyluronic acid residues in the pectic polysaccharide homogalacturonan (HGA) is catalyzed by an enzyme commonly referred to as pectin methyltransferase. A pectin methyltransferase from microsomal membranes of tobacco (Nicotiana tabacum) was previously characterized (F. Goubet, L.N. Council, D. Mohnen [1998] Plant Physiol 116: 337-347) and named HGA methyltransferase (HGA-MT). We report the solubilization of HGA-MT from tobacco membranes. Approximately 22% of the HGA-MT activity in total membranes was solubilized by 0.65% (w/v) 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid containing 1 mM dithioerythritol. The addition of phosphatidylcholine and the methyl acceptors HGA or pectin (30% degree of esterification) to solubilized enzyme increased HGA-MT activity to 35% of total membrane-bound HGA-MT activity. Solubilized HGA-MT has a pH optimum of 7.8, an apparent K(m) for S-adenosyl-L-methionine of 18 microM, and an apparent V(max) of 0. 121 pkat mg(-1) of protein. The apparent K(m) for HGA and for pectin is 0.1 to 0.2 mg mL(-1). Methylated product was solubilized with boiling water and ammonium oxalate, two conditions used to solubilize pectin from the cell wall. The release of 75% to 90% of the radioactivity from the product pellet by mild base treatment showed that the methyl group was incorporated as a methyl ester rather than a methyl ether. The fragmentation of at least 55% to 70% of the radiolabeled product by endopolygalacturonase, and the loss of radioactivity from the product by treatment with pectin methylesterase, demonstrated that the bulk of the methylated product produced by the solubilized enzyme was pectin.
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PMID:Solubilization and partial characterization of homogalacturonan-methyltransferase from microsomal membranes of suspension-cultured tobacco cells. 1048 84

Pectin methyltransferase (PMT) catalyzing the transfer of the methyl group from S-adenosyl-L-methionine (SAM) to the C-6 carboxyl group of galactosyluronic acid residues in pectin was found in a membrane preparation of etiolated hypocotyls from 6-d-old soybean (Glycine max Merr.). The enzyme was maximally active at pH 6.8 and 35-40 degrees C, and required 0.5% (w/v) Triton X-100. The incorporation of the methyl group was significantly enhanced by addition of a pectin with a low (22%) degree of methyl-esterification (DE) as exogenous acceptor substrate. The apparent Michaelis constants for SAM and the pectin (DE22) were 0.23 mM and 66 microg x ml(-1), respectively. Attachment of the methyl group to the carboxyl group of the pectin via ester linkage was confirmed by analyzing radiolabeled product from incubation of the enzyme with [14C]methyl SAM and the acceptor pectin. Size-exclusion chromatography showed that both enzymatic hydrolysis with a pectin methylesterase and a mild alkali treatment (saponification) led to the release of radioactive methanol from the product. Enzymatic hydrolysis of the product with an endopolygalacturonase degraded it into small pectic fragments with low relative molecular mass, which also supports the idea that the methyl group is incorporated into the pectin. The soybean hypocotyls were fractionated into their cell wall components by successive extraction with water, EDTA, and alkali treatment. Among the resulting polysaccharide fractions, high PMT activity was observed when a de-esterified polysaccharide derived from the EDTA-soluble fraction (the pectic fraction) was added as an alternative acceptor substrate, indicating that the enzyme may be responsible for producing methyl-esterified pectin in vivo.
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PMID:Characterization of pectin methyltransferase from soybean hypocotyls. 1080 50

S-adenosylmethionine (SAM) is the substrate used in the methylation of homogalacturonan (HGA) in the Golgi apparatus. SAM is synthesized in the cytosol, but it is not currently known how it is then transported into the Golgi. In this study, we find that HGA methyltransferase is present in Golgi-enriched fractions and that its catalytic domain faces the lumen of this organelle. This suggests that SAM must be imported into the Golgi. We performed uptake experiments using [methyl-(14)C]SAM and found that SAM is incorporated into the Golgi vesicles, resulting in the methylation of polymers that are sensitive to pectinase and pectin methylesterase but not to proteases. To avoid detecting the transfer reaction, we also used [carboxyl-(14)C]SAM, the uptake of which into Golgi vesicles was found to be sensitive to temperature, detergents, and osmotic changes, and to be saturable with a K(m) of 33 microm. Double-label uptake experiments using [methyl-(3)H]SAM and [carboxyl-(14)C]SAM also revealed a time-dependent increase in the (3)H to (14)C ratio, suggesting that upon transfer of the methyl group, the resulting S-adenosylhomocysteine is not accumulated in the Golgi. SAM incorporation was also found to be inhibited by S-adenosylhomocysteine, whereas UDP-GalA, UDP-GlcA, and acetyl-CoA had no effect. DIDS, a compound that inhibits nucleotide sugar transporters, also had little effect upon SAM incorporation. Interestingly, the combination of UDP-GalA + acetyl-CoA or UDP-GlcA + acetyl-CoA produced a slight increase in the uptake of SAM. These results support the idea that a SAM transporter is required for HGA biosynthesis.
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PMID:The import of S-adenosylmethionine into the Golgi apparatus is required for the methylation of homogalacturonan. 1776 97

The structure of the cell wall has a major impact on plant growth and development, and alteration of cell wall structural components is often detrimental to biomass production. However, the molecular mechanisms responsible for these negative effects are largely unknown. Arabidopsis (Arabidopsis thaliana) plants with altered pectin composition because of either the expression of the Aspergillus niger polygalacturonase II (AnPGII; 35S:AnPGII plants) or a mutation in the QUASIMODO2 (QUA2) gene that encodes a putative pectin methyltransferase (qua2-1 plants), display severe growth defects. Here, we show that expression of Arabidopsis PEROXIDASE71 (AtPRX71), encoding a class III peroxidase, strongly increases in 35S:AnPGII and qua2-1 plants as well as in response to treatments with the cellulose synthase inhibitor isoxaben, which also impairs cell wall integrity. Analysis of atprx71 loss-of-function mutants and plants overexpressing AtPRX71 indicates that this gene negatively influences Arabidopsis growth at different stages of development, likely limiting cell expansion. The atprx71-1 mutation partially suppresses the dwarf phenotype of qua2-1, suggesting that AtPRX71 contributes to the growth defects observed in plants undergoing cell wall damage. Furthermore, AtPRX71 seems to promote the production of reactive oxygen species in qua2-1 plants as well as plants treated with isoxaben. We propose that AtPRX71 contributes to strengthen cell walls, therefore restricting cell expansion, during normal growth and in response to cell wall damage.
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PMID:The Arabidopsis Class III Peroxidase AtPRX71 Negatively Regulates Growth under Physiological Conditions and in Response to Cell Wall Damage. 2646 18

Guanidinoacetic acid (GAA) can improve the growth performance of bulls. This study investigated the influences of GAA addition on growth, nutrient digestion, ruminal fermentation and serum metabolites in bulls. Forty-eight Angus bulls were randomly allocated to experimental treatments, that is, control, low-GAA (LGAA), medium-GAA (MGAA) and high-GAA (HGAA), with GAA supplementation at 0, 0.3, 0.6 and 0.9 g/kg DM, respectively. Bulls were fed a basal diet containing 500 g/kg DM concentrate and 500 g/kg DM roughage. The experimental period was 104 days, with 14 days for adaptation and 90 days for data collection. Bulls in the MGAA and HGAA groups had higher DM intake and average daily gain than bulls in the LGAA and control groups. The feed conversion ratio was lowest in MGAA and highest in the control. Bulls receiving 0.9 g/kg DM GAA addition had higher digestibility of DM, organic matter, NDF and ADF than bulls in other groups. The digestibility of CP was higher for HGAA than for LGAA and control. The ruminal pH was lower for MGAA, and the total volatile fatty acid concentration was greater for MGAA and HGAA than for the control. The acetate proportion and acetate-to-propionate ratio were lower for MGAA than for LGAA and control. The propionate proportion was higher for MGAA than for control. Bulls receiving GAA addition showed decreased ruminal ammonia N. Bulls in MGAA and HGAA had higher cellobiase, pectinase and protease activities and Butyrivibrio fibrisolvens, Prevotella ruminicola and Ruminobacter amylophilus populations than bulls in LGAA and control. However, the total protozoan population was lower for MGAA and HGAA than for LGAA and control. The total bacterial and Ruminococcus flavefaciens populations increased with GAA addition. The blood level of creatine was higher for HGAA, and the activity of l-arginine glycine amidine transferase was lower for MGAA and HGAA, than for control. The blood activity of guanidine acetate N-methyltransferase and the level of folate decreased in the GAA addition groups. The results indicated that dietary addition of 0.6 or 0.9 g/kg DM GAA improved growth performance, nutrient digestion and ruminal fermentation in bulls.
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PMID:Effects of guanidinoacetic acid supplementation on growth performance, nutrient digestion, rumen fermentation and blood metabolites in Angus bulls. 3258 Aug 13