D-galactan

Benzyl derivatives of (1 6)-a-D-glucan, (l->6)-a-D-mannan, and (l-> 6)-a-D-galactan have been studied in 1,4-dioxane. These derivatives have complex and interesting c.d. spectra due to the ww transition of the chromophore with resolved vibrational structure. However, a conformational interpretation of these interesting spectra is not possible at this time. 

Our standard incorporation assays contained resuspended particulate enzyme, labelled UDP-Gal (0.1 mM) and (10 mM) in resuspension buffer (Tris, pH 7.5). After incubation, reaction mixtures were heated briefly to 100°C and soluble lupin galactan was added, to ensure the precipitation of small amounts of galactan formed in the en me reaction and dissolved during the heating step. Precipitation of macromolecular products was achieved by adding methanol to a final concentration of 70%. The pellet was freed of soluble labelled products, including residual UDP-Gal, by repeated extraction with hot 70% methanol and was then analysed for labelled (l- )-P-D-galactan. The supernatant was analysed for soluble labelled products. 

Galactan synthase in relation to (l->4)-P-D-galactan levels in tissue cell walls... 

The D-arabino-D-galactan of cells of the insect protozoon Crithidia fasciculata contains /3-D-(l—>3)-linked D-galactopyranosyl main-chain units, some of which are unsubstituted others are substituted at 0-2 by (single-unit) D-arabinopyranosyl groups. The 13C-n.m.r. spectrum shows that these are only partial structures, as the C-l region contained 8 signals.125... 

Comparison of Endolytic Hydrolases That Depolymerize l,4- d-D-Mannan, 1,5-a-L-Arabinan, and 1,4- -D-Galactan... 

The first polymerizations reported by Kops and Schuerch147 were those of l,4-anhydro-2,3,6-tri-0-methyl-/3-D-galactopyranose and 1,4-anhydro-2,3-di-0-methyl-a -L-arabinopyranose. The latter compound was slightly contaminated with l,4-anhydro-2,3-di-0-methyl-a-D-xy-lopyranose, but the course of the polymerization could nevertheless be monitored reasonably accurately. For the most part, the polymerizations were conducted at 10% concentration (g/mL) in dichloro-methane, or aromatic hydrocarbons, with 1-5 mol% of phosphorus pentafluoride, or boron trifluoride etherate. At low temperature (—78 to —97°), the d.p. of both polymers produced was —90 at increasing temperatures of polymerization, termination processes became more severe, and the d.p. lower. Usually, the reaction times were long (perhaps unnecessarily so), and the conversions were 50 to 90%. The specific rotations of the D-galactans prepared at —28 and —90° differ by only —10° ( — 85 to — 95°), but those of the L-arabinans varied from + 6... 

Structural aspects of L-arabino-D-galactan glycoprotein from radish leaves have been studied by using /3-D-galactonase, /J-D-galactosidase, and a-L-arabinofuranosidase, in conjunction with methylation analysis.3786... 

The biosynthesis of other O-specific polysaccharides has still not been investigated. The only additional example of demonstration of such a process is in the formation of (l->3)-a-D-galactan, the Ol antigen of Klebsiella.333 UDP-Gal was identified as the glycosyl donor in the reaction, but further details of the mechanism remain unclear. 

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