Peter Albersheim

3-deoxy-d-lyxo-2-heptulosaric acid, a component of the plant cell-wall polysaccharide rhamnogalacturonan-II☆☆☆

Abstract 3-Deoxy- d - lyxo -heptulosaric acid (DHA) has been identified as a component of plant cell walls. This sugar was found in the pectic polysaccharide rhmanogalacturonan-II as a component of the disaccharide β- l -Ara f -(1→5)- d -DHA p . The structural formula and linkage position of DHA were determined by mass spectrometry of several derivatives. The lyxo configuration was determined by 1 H-n.m.r. spectroscopy of a derivative of the isolated disaccharide. The d configuration was determined by partial degradation of DHA to l -glyceric acid. DHA was found to be present in the primary cell walls of many higher plants, including several dicots, two monocots, and a gymnosperm, but was not detected in two bacterial lipopolysaccharides.

Structural features of the plant cell-wall polysaccharide rhamnogalacturonan-II

Abstract Rhamnogalacturonan-II (RG-II), isolated from the cell walls of suspension-cultured sycamore cells, has been further characterized. End-group analysis of RG-II showed that the polysaccharide contains about 30 glycosyl residues. Some 28 residues have been found as constituents of well characterized oligosaccharide fragments of RG-II. RG-II was treated with lithium metal dissolved in ethylenediamine to degrade the glycosyluronic acid residues. The major product was isolated, characterized, and shown to be the triglycosylalditol α-Xyl-(1→3)-α-Fuc-(1→4)-β-Rha-(1→3 1 )-apiitol. This tetrasaccharide fragment of RG-II has three residues in common with a previously characterized heptasaccharide that had been derived from RG-II by partial hydrolysis with acid. RG-II was found to contain a large number of branched galactosyluronic acid residues that have not yet been identified as components of oligosaccharide fragments, although they are undoubtedly part of an octa(galactosyluronic acid) fragment generated by partial acid hydrolysis. The results of sequential partial acid hydrolysis provided evidence that, in RG-II, the extremely acid-labile 3-deoxy- d - manno -2-octulosonic-acid and 3-deoxy- d - lyxo -2-heptulosaric acid residues are attached to O-3 of 3,4-linked galactosyluronic acid residues, and that the mildly acid-labile apiofuranosyl residues are attached to O-2 of 2,4-linked galactosyluronic acid residues. These and previously published data suggested that RG-II has a highly branched structure, arranged around an α-(1→4)-linked galactosyluronic acid backbone.

A fluorescence assay for enzymes that cleave glycosidic linkages to produce reducing sugars

A rapid, facile, and sensitive assay has been developed for enzymes that generate reducing sugars. The assay is a modification of a method for post-HPLC column derivatization and detection of reducing sugars and is carried out in a single test tube. The assay is useful for large numbers of samples, such as those produced during purification of enzymes. Less than 500 pmol of reducing sugar can be quantitatively measured. The assay reported here is at least 10 times more sensitive than either the commonly employed parahydroxybenzoic acid hydrazide method or the recently reported bicinchoninate method, and 50 times more sensitive than the Nelson-Somogyi method.