Methyl esterification

Special care must be taken in the case of betacyanins acylated with dicarboxylic acids such as malonic acid, i.e., phyllocactin. Upon acidification in methanol, methyl-esterification may easily proceed, thus generating a new pigment that is not genuine... 

Mort, A.J., Qiu, F., and Maness, N.O. (1993) Determination of the pattern of methyl esterification in pectin. Distribution of contiguous nonesterified residues. CarbohydrJies. 247 21-35. 

METHYL-ESTERIFICATION, DE-ESTERIFICATION AND GELATION OF PECTINS IN THE PRIMARY CELL WALL. 

In this review we fitcus on the biosynthetic mechanisms by vririch the methyl-esterification of the galacturonan chains in pectins is controlled. We go on to examine the structure of the pectic gels that are formed and their relationsh with the stresses carried by specific parts of the cell wall. 

The possibility that the initial degree of methyl-esterification might be controlled by the properties of the methyltransferase enzymes was examined partial characterisation of these enzymes in suspension-cultured cells of fiax. Pectin methyltransferases beii enzymes characteristic of the Golgi apparatus [22], microsomes were fiactionated daily for ten days from suspension-cultured flax cells and incubated in the presence of C-SAM, the universal donor of methyl groups. 

Thus pectins in muro contain most elements of the cable model but have additional features due to esterification (acetyl- as well as methyl-) and branching. The ionic junction zones are similar to those of calcium pectate gels in vitro but also contam methyl-esterified junctions, and most of the single chains probably have a relatively high degree of methyl-esterification. 

Methyl esterification When prohexadione was treated with methanolic HCl (3%, w/v) or sulfuric acid-methanol (1 %, v/v) under reflux at 75 °C for 60 min, or with BFs-methanol (14%, w/v) under reflux at 75 °C for 30 min, the yield of the methyl ester of prohexadione was 95,93 and 82%, respectively (prohexadione, 10 qg, volume 2 mL of methanolic HCl, 2 mL of sulfuric acid-methanol and 1 mL of BFs-methanol). A solution of 1% (v/v) sulfuric acid in methanol was chosen for ease of preparation. Even if prohexadione was treated with 1% sulfuric acid in methanol at room temperature for 12h, the yield of prohexadione methyl ester was not different from that under reflux conditions as described in Section 6.3. The conditions for methyl esteriflcation in Section 6.3 were chosen because of shortening of the analysis time and the reproducibility of the reaction yield in residue analysis samples which could contain large quantities of contaminants. 

The improvement of its activity and stability has been approach by the use of GE tools (see Refs. [398] and [399], respectively). A process drawback is the fact that the oxidation of hydrophobic compounds in an organic solvent becomes limited by substrate partition between the active site of the enzyme and the bulk solvent [398], To provide the biocatalyst soluble with a hydrophobic active site access, keeping its solubility in organic solvents, a double chemical modification on horse heart cytochrome c has been performed [400,401], First, to increase the active-site hydrophobicity, a methyl esterification on the heme propionates was performed. Then, polyethylene glycol (PEG) was used for a surface modification of the protein, yielding a protein-polymer conjugates that are soluble in organic solvents. 

Hemoglobin is another heme-containing protein, which has been shown to be active towards PAH, oxidation in presence of peroxide [420], This protein was also modified via PEG and methyl esterification to obtain a more hydrophobic protein with altered activity and substrate specificity. The modified protein had four times the catalytic efficiency than that of the unmodified protein for pyrene oxidation. Several PAHs were also oxidized including acenaphthene, anthracene, azulene, benzo(a)pyrene, fluoranthene, fluorene, and phenanthrene however, no reaction was observed with chrysene and biphenyl. Modification of hemoglobin with p-nitrophenol and p-aminophenol has also been reported [425], The modification was reported to enhance the substrate affinity up to 30 times. Additionally, the solvent concentration at which the enzyme showed maximum activity was also higher. Both the effects were attributed to the increase in hydrophobicity of the active site. 

However, they varied in content of neutral sugars and extent of methyl-esterification. The presence of rham-nose in the backbone of pectin was believed to create kinks which probably disrupted helical stretches of the... 

The evidence available suggests that the polymer in Lemna consists of an a-( 1— 4)-linked galacturonan backbone, with side chains of apiobiose, D-Api/-(1— 3)-D-Api/. The degree of methyl esterification of the galacto-syluronic residues is low. The nature of the galactosyluronic-apiosyl linkage has not yet been established. 

Methyl esterification takes place after poly(galacturonic acid) is formed, and Kauss and coworkers315-317 showed that the mung-bean particulate-fraction that contains the galactosyluronic transferase also contains an enzyme responsible for methylating carboxyl groups of poly(galacturonic acid). The methyl donor for this reaction is S-adeno-syl-L-methionine. 

Purity was confirmed by gel-filtration using a HPLC column packed with Asahipak GS-520HQ and elution with 100 mM sodium phosphate buffer containing 300 mM sodium chloride (pH 6.7). The content of total protein, total sugars, uronic acids, sulfates, nucleic acids, phosphate or fatty acids was assayed by the BCA [32] and Lowry method [33], the phenol-sulfuric acid method [34], the Blumenkrantz method [35], nephelometry [36], absorption at 260 nm, the Bartlett method [37] and the GLC method after methyl-esterification [38], respectively. 

Due to reduction or lack of hydrogen bonding, carbonyl carbon nuclei of amides [313-315], anhydrides [316], esters [310-312], and halides [317] display smaller shift values relative to the parent acids (Tables 4.34 and 4.35). Methyl esterification shieldings are about — 6+1 ppm for mono- and — 1.5 + 1 ppm for diesters, reflecting weaker hydrogen bonding in dicarboxylic acids [316] Taking the methoxy carbon as a /i effect... 

Calculate degree of methyl esterification using the following formula ... 

A certain amount of evidence shows that methyl group metabolism may be affected as a result of auxin treatment—generally increased pectin-methyl esterification is observed (7). Though pectin-methyl esterification may be correlated with increased wall plasticity, there are as yet no obvious connections between general methyl group availability on the one hand and permeability, peroxidation, and mitosis on the other. 

N. O. Maness, J. D. Ryan, and A. J. Mort, Determination of the degree of methyl esterification of pectins in small samples by selective reduction of esterified galacturonic acid to galactose, Anal. Biochem., 185 (1990) 346-352. 

Hydrolysis and Methyl Esterification Dadan Kusdiana and Shiro Saka ... 

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