Smith degradation of gum exudates from some prosopis species

Other Plant Polysaccharides

“…4] is present in hydrolysates from A. pycnantha gum, which also, as is generally the case with arabino-3,6-galactans, included 24 and 25. The residues shown by methylation analysis to be present in the gums of A. podalyriaefolia and A. difformis (238) (247). Smith degradations in three stages give rise to galactose-rich products having molecular weights of approximately 36,000, 12,000, and 6000 at the first stage, 11,000 and 5500 at the second, and 4800 at the third, indicating that such sugar residues as join the (1->3)-linked main-chain residues are in part substituted by one or two other sugar units, which at first protect them from periodate oxidation.…”

“…There may also be a relatively small number of side chains of considerable length (10 sugar residues), as has been shown by alkaline degradation of a larch arabinogalactan preparation (277), and the possibility of acid-labile L-Ara/residues occurring in the main chains (272) receives support from the galactose/arabinose molar ratio and the identification of five-carbon metasaccharinic (3-deoxypentonic) acids in the products of hydrolysis of the alkali-degraded arabinogalactan. It is difficult, therefore, to present a coordi nated picture of the total structure of any of these polysaccharides.…”

“…residues. The molecu lar weights of the structural subunits thereby separated from one another are estimated to be 4000, since the Smith-degraded polysaccharide isolated (209,210) from each of the samples has a molecular weight of -2200 and it can be seen from 15 that the peripheral sugar residues removed on Smith degradation would constitute about 50% of the total.…”

“…Of these gum exudates those from A. pycnantha, A. podalyriaefolia, A. difformis, and A. mabellae form a coherent group resem bling each other in [α] Ό (ranging from -9 to + 5°), average molecular weight (M w 30,000 or less), and sugar composition. They are essentially arabinogalactans (galactose content -70%, arabinose -25%), but all contain uronic acid (6% or less) and rhamnose (1 -2%) as well (236)(237)(238)(239). Measurement of the molecular weight distributions of A. pycnantha gum samples from different localities and from different branches of one tree has shown that, although average molecular weight varies, there are a number of compo nents (approximating multiples of 6000 in molecular weight) in each polymolecular sample that are present in various proportions.…”

“…In most respects the gum (249) of A. longifolia (Subseries VIII), which species has been placed, (250) on the basis of computer analysis of blocks of numerous characteristics, in the same botanical group as A. saligna, is closely similar to that of A. saligna (Bentham Subseries VI). There is evidence (249) to support the transfer of A. saligna to Subseries VIII. The units present in the gums of A. rubida and A. retinoides, which are placed botanically in the same subseries (VI) and group (vi) as A pycnantha (251), are quite similar according to methylation analysis (236), although their molecular weights are high (246).…”