Degree of methylation

The commercial samples of pectins mainly used as food additives represent modified forms of the natural polymers due to the conditions of extraction. Nevertheless, it is usually recognized two categories of pectins the high methoxyl pectins (HM) with a degree of methylation DM>50% forming gels at low pH in presence of saccharose to reduce the water activity and the low methoxyl pectins (LM with DM<50%) forming gel in presence of calcium [4]. 

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. 

An important feature concerned the degree of methylation (dm). A value of 81 % was obtained after acid extraction and a very high value of 91 % was obtained for the pectins from extruded fibres. This is an unusual value for a dm and this result shows that extrusion-cooking had a very limited effect on the methylation of the pectin. 

Degree of methylation (DM%) of total pectin of carrot alcohol insoluble sohds (AIS) was decreased from 60.73% for fresh carrots to 48.70, 44.62 and 43.83% for canned carrots preheated at 65°C for 15. 30 and 60 min, respectively (Fig. 2). Similar levels of demethylation were also reported in potato (Bartolome and Hoff, 1972), in carrots (Lee et al., 1979) and in snap beans (Adams and Robertson, 1987) when they were blanched at low temperature between 65°C and 70°C. 

Figure 2. Degree of methylation (DM) and degree of acetylation (DAc) of the total pectin of fresh and canned carrots...

Effect of CaCl2 on firmness, alcohol insoluble solids content and degree of methylation (DM%) of carrots canned by conventional and by a new process... 

The terms for the purified apple pectins indicate the degree of methylation. 

Commercial Rapid Set citrus pectin (864 mg galacturonic acid per g, degree of methylation 73) was from SBI (Beaupte, France). 

Figure 3. Determination of the optimal parameters of PelZ activity. A pectate lyase activity in a reaction medium containing PGA 0.05%, CaCl2 0.2 mM and Tris-HCl 50 mM at various pH. B pectate lyase activity in a reaction medium containing PGA 0.05%, Tris-HCl 50 mM pH 8.5 and increasing concentrations of CaCl2- C pectate lyase activity in a reaction medium containing CaCl2 0.2 mM, Tris-HCl 50 mM pH 8.5 and as substrate either PGA 0.05% or pectins 0.05%, with different degrees of methylation (from Copenhagen Pectin).

For the oxidations, the cathodic shifts (P— As- Sb- Bi) are nearly the same for the tetramethyl series and the octamethyl series. Since the shifts are independent of the degree of methyl substitution, these shifts can be used to estimate the 1/2 values for the series of unsubstituted diheteroferrocenes from the experimental value for l,l -diarsaferrocene. 

The logX values were found to decrease as the degree of methylation increased. Analysis of the data led to the conclusion that the first two protonations were on the terminal tertiary nitrogen, followed by the others on the inner nitrogens60. 

Reuter G, Spierer P (1992) Position effect variegation and chromatin proteins. Bioessays 14 605—612 Rice JC, Briggs SD, Ueberheide B, Barber CM, Shabanowitz J, Hunt DF, Shinkai Y, Allis CD (2003) Histone methyltransferases direct different degrees of methylation to define distinct chromatin domains. Mol Cell 12 1591-1598... 

Alkyl-substituted radicals. In the series of alkylated methyl radicals, stabilization increases with increasing degree of methylation, going parallel... 

The same degree of methylation as by refluxing with methanol was achieved by blowing a stream of methanol vapor and nitrogen over the carbon heated to 120°. 

Fig. 9.2 Representative examples of the methylation-specific polymerase chain reaction (MSP) analyses for gene promoter regions. Lanes Lf and M indicate the presence of unmethylated and methylated template, respectively. Placental DNA (PDNA) and in vitro methylated DNA (IMD) served as negative and positive controls, respectively. Water (H) was used to detect contamination. Samples 1, 3, 4, and 7 indicate the presence of a methylated promoter DNA with various degrees of methylation, and samples 2, 5, and 6 represent an unmethylated promoter...

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