Xylosyl Units Research Articles

Saponins of pericarps of Chinese Sapindus delavayi (Pyi-shiau-tzu), a source of natural surfactants.

From pericarps of Sapindus delavayi (Chinese name : Pyi-shiau-tzu, Japanese name : Hishoushi)collected in Yunnan, China, several monodesmosides, 2-4 and 8-10 were isolated, all of which have already been isolated from pericarps of S. mukurossi (Japanese name : Enmeihi). Besides these known saponins, Sapenins 11 (a new saponin named hishoushi-saponin A), 13 and 14 (a new saponin named hishoushi-saponin Ee) were isolated from Pyi-shiau-tzu and their structures were elucidated to be as follows : 11, oleanolic acid 3-O-α-L-arabinopyranosyl-(1→3)-α-L-rhamnopyranosyl-(1→2)-α-L-arabinopyranoside; 13, oleanolic acid 3-0-β-D-xylopyranesyl-(1→3)-x-L-rhamnopyranosyl-(1→2)-α-L-arabinopyranoside (identica with the prosapogenin of the saponins from Clematis chinensis); 14, an acetate of sapindoside B (3) in which the acetyl group is located at the 3-hydroxyl group of the terminal xylosyl unit. It was found that the content of acylated saponins such as 14 in Pyi-shiau-tzu is higher than that in Enmeihi. Two diacetylated saponins, 15 and 16, were isolated from Pyi-shiau-tzu not in an impure state and their structures were deduced by nuclear magnetic reonance spectrometry. It is noteworthy that in contrast to Enmeihi, no bisdesmoside was detected in Pyi-shiau-tzu.

Saponins of pericarps of Sapindus mukurossi Gaertn. and solubilization of monodesmosides by bisdesmosides.

From pericarps of Sapindus mukurossi (Japanese name : Enmei-hi), saponins of hederagenin (1), 2-7, 9, 11 and 12 were isolated along with sapindosides A (10) and B (8), both of which have already been isolated from this crude drug. Saponins 7 and 9 were identified as α-L-arabinopyranosyl (1→3)-α-L-rhamnopyranosyl (1→2)-α-L-arabinopyranoside and α-L-arabinofuranosyl (1→3)-α-L-rhamnopyranosyl (1→2)-α-L-arabinopyranoside of 1, respectively, both of which were recently isolated from Lecaniodiscus cupanoides by Sandberg et al. New saponins named mukurozi-saponins E1 (11) and G (12) were proved to be the mono-acetate of 8 and the di-acetate of 7, respectively. By means of mass and 13C nuclear magnetic resonance (NMR) spectroscopy, the locations of the acetyl groups of 11 and 12 were established to be at the 4-hydroxyl group of the xylosyl unit of 8 and at the 3, 4-hydroxyl groups of the terminal arabinosyl unit of 7, respectively. The other new saponins, named mukurozi-saponins X (6), Y1 (5) and Y2 (4), were revealed to be β-sophorosyl esters of 10, 8 and 7, respectively, by comparison of the mass and 13C NMR spectra with those of the β-sophorosyl ester of 1 (13), which was synthesized from 1 as a reference compound for the study of the anomalous glycosylation shifts. Studies on the structures of the remaining saponins, 2 and 3, are in progress. The water solubilities of the monodesmosides, 7-9, which cause remarkable enhancement of the absorption of sodium ampicillin from rat intestine and rectum, were greatly increased by the bisdesmosides, 4-6.

Cooperative action of β-glucan synthetase and UDP-xylose xylosyl transferase of Golgi membranes in the synthesis of xyloglucan-like polysaccharide

Golgi membranes of pea seedling tissue contain a UDP xylose:polysaccharide xylosyl transferase, the action of which is stimulated by UDP glucose. In the presence of both nucleotide-sugars a heteropolysaccharide containing both xylose and glucose (xyloglucan) is produced. Transfer of xylose and glucose units is presumed to be due to separate enzymes, because their properties differ in a number of respects. Xylosyl units appear to be transferred to a glucan core polysaccharide that is produced from UDP glucose by β-1,4-glucan synthetase. This, rather than cellulose biosynthesis, is inferred to be the in vivo role of Golgi membrane β-1,4-glucan synthetase.

Metabolic Studies on Intermediates in the myo-Inositol Oxidation Pathway in Lilium longiflorum Pollen

myo-Inositol-linked glucogenesis in germinated lily (Lilium longiflorum Thunb., cv. Ace) pollen was investigated by studying the effects of added l-arabinose or d-xylose on metabolism of myo-[2-(3)H]inositol and by determining the distribution of radioisotope in pentosyl and hexosyl residues of polysaccharides from pollen labeled with myo-[2-(14)C]inositol, myo-[2-(3)H]inositol, l-[5-(14)C]arabinose, and d-[5R,5S-(3)H]xylose.myo-[2-(14)C]Inositol and l-[5-(14)C]arabinose produced labeled glucose with similar patterns of distribution of (14)C, 35% in C1, and 55% in C6. Arabinosyl units were labeled exclusively in C5. Incorporation of (3)H into arabinosyl and xylosyl units in pollen labeled with myo-[2-(3)H]inositol was repressed when unlabeled l-arabinose was included in the germination medium and a related (3)H exchange with water was stimulated. Results are consistent with a process of glucogenesis in which the myo-inositol oxidation pathway furnishes UDP-d-xylose as a key intermediate for conversion to hexose via free d-xylose and the pentose phosphate pathway.Additional evidence for this process was obtained from pollen labeled with d-[5R,5S-(3)H]xylose or myo-[2-(3)H]inositol which produces d-[5R-(3)H]xylose. Glucosyl units from polysaccharides in the former had 11% of the (3)H in C1 and 78% in C6 while glucosyl units in the latter had only 4% in C1 and 78% in C6. Stereochemical considerations involving selective exchange with water of prochiral-R (3)H in C1 of fructose-6-P during conversion to glucose provide explanation for observed differences in the metabolism of these 5-labeled xyloses.Incorporation of (3)H from myo-[2-(3)H]inositol into arabinosyl and xylosyl units of pollen polysaccharides was unaffected by the presence of unlabeled d-xylose in the medium. Exchange of (3)H with water was greatly affected, decreasing from a value of 21% exchange in the absence of unlabeled d-xylose to 5% in the presence of 6.7 mmd-xylose.d-Xylose was rapidly utilized for glucogenesis by germinated pollen tubes. This observation supports the view that free d-xylose is an important intermediate following breakdown of UDP-d-xylose during myo-inositol-linked glucogenesis.

Xylosyltransferases in Cryptococcus laurentii

Abstract A particle-bound enzyme preparation from the fungus imperfectus, Cryptococcus laurentii, contains at least two different xylosyltransferases. One of these catalyzes the transfer of xylosyl units from UDP-xylose to endogenous cell envelope glycoproteins. The enzyme requires the disaccharide, 3-O-α-d-mannosyl-d-mannose, or the same structure at the terminal nonreducing end of an oligosaccharide as an acceptor. The xylosyl residue is transferred to the pentultimate mannosyl at the nonreducing end of the acceptor with the formation of a β-1,2 linkage. The product, 3-O-α-d-mannosyl-(2-O-β-d-xylosyl)-d-[3-14C]mannose, was synthesized, reduced with sodium borohydride, oxidized with periodate, again reduced, and then hydrolyzed. This procedure led to the formation of [14C]erythritol confirming the structure of the product. The xylosyltransferase has a pH optimum of 6.0 to 6.5. The apparent Km values for UDP-xylose and mannobiose are 1.4 mm and 19 mm, respectively. These properties, as well as the nature of the product formed, stability of the enzyme at 38°, and inhibition by nucleotides, clearly differentiate between this enzyme and a second xylosyltransferase that has been described for C. laurentii (Cohen, A., and Feingold, D. S. (1967) Biochemistry 6, 2933).