Pectins molecular sizes

Two characteristics of the lyase that we have purified may be significant. First, the small molecular size of the protein may confer it a high mobility that could be helpful to its movement through host cell walls. In second place, it is an endo-type enzyme, fact that has been considered essential for maceration of plant tissues [35]. In this sense it is noteworthy that between the battery of pectic enzymes produced by FORL, this pectin lyase is the only protein that behaves as an endo-type. 

There is no major advance which can be reported in our knowledge of protopectinases. The possibility of the existence of a protopectinase different from PG seems now somewhat more remote than it was ten years ago. As stated above, the trend in thinking about protopectin is definitely in the direction that protopectin is not a specific cellulose-pectinic acid compound but pectinic acid which is insoluble either on account of large molecular size or due to the effect of polyvalent cations or both. In this sense there is really no need to assume the existence of a separate protopectinase. There is little doubt that this uncertainty is in a large degree attributable to the lack of precise knowledge of protopectin. 

Hourdet, D., and Muller, G. (1991). Solution properties of pectin polysaccharides II. Conformation and molecular size of high galacturonic acid content isolated pectin chains. Carbohydr. Polym. 16 113-135. 

The first probable values for the molecular size of the native pectins from apple and sugar beet were obtained by Schneider and co-workers.71 These workers prepared the nitro- and acetyl-derivatives in order to avoid the anomalous behavior due to charge effects which occurred using the unsubstituted polysaccharides. From osmotic and viscometric measurements on the nitrate, values for the molecular weight of 30,000-100,000 were found, the constant Km in Staudinger s equation being 6(10)-4. Viscometric measurements indicated that there was little difference in size between the two derivatives. 

Hourdet, D. and Muller, G. 1991. Solution properties of pectin polysaccharides—HI molecular size of heterogeneous pectin chains. Cahbration and application of SEC to pectin analysis, Carbohydrate-Polymers, 16(4) 409-432. 

Figure 3 Effect of ionic calcium addition on average droplet sizes dA3 and creaming stability of D-limonene emulsions (10 vol% oil, ionic strength 0.2 M, pH 4.7) stabilized by depolymerized pectin molecular weight 70 kg/mol...

In experimentel animals, methylcellulose injection leads to hypertension, due to extensive methylcellulose thesaurosis of the glomerular endothelium (Hall and Hall 1961). Comparable hypertension and nephrotoxicity have been produced by injection of polyvinyl alcohol (Hall and Hall 1965). The pathogenic effects depended more on molecular size than on chemical structure. Similarly, dogs and rabbits injected with pectin showed atheromatous changes and thesaurosis with foam cellular storage phenomena in spleen, liver, and kidneys (Hueper 1942). 

Two new ion-exchange polysaccharides have been developed for use in the fractionation of polysaccharides and other biopolymers. Pectins from the bark of Salix alba were separated on columns of 0-(3-diethylamino-2-hydroxy-propyl)starch (DEAHP-starch) into six components differing in uronic acid content and in molecular size. The corresponding cellulose derivative (DEAHP-cellulose) was used in the fractionation of glucomannans from the same source. The methodology and the instrumentation used in ion-exchange chromatography... 

For a century the development of pectin chemistry was severely handicapped by the aim of investigators to identify its structure in terms of a constant, relatively small molecular size . It is clear today that any sample of a pectic substance is in reality a mixture of polygalacturonic acids of various... 

Figure 3 Size fractionation of EDTA-soluble polyuronides from Rutgers and transgenic fruit juice processed by cold- and hot-break methods. Pectin from processed juice was extracted as ethanol-insoluble solids and size fractionated on a Sepharose CL4B column. Under the same chromatographic conditions, elution of the branched dextrans with average molecular mass 2000, 500, 252, 151, 40 and 17.7 kD-peaked in fraction number 46, 50, 54, 62, 67 and 72, respectively. Modified from Thakur et al. [23].

A decrease in the pectic molecular weight by pectin lyase resulted in an increase in the activity of PAE (Figure 2). This could be caused by easier access of the enzyme to the substrate, but PAE is not limited in its action by the substrate size as was found for FAE. 

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