David J. Manners

Recent developments in our understanding of amylopectin structure

Abstract The molecular structure of amylopectin can be described in terms of various parameters, e.g. average chain length, exterior and interior chain lengths, ratio of A-chains to B-chains and chain profile. Enzymic methods for the measurement of these parameters are critically discussed. The overall results are then considered in relation to the cluster model for amylopectin, which has emerged in recent years as the most probable molecular model.

The structure of a β-(1→3)-d-glucan from yeast cell walls

Yeast glucan as normally prepared by various treatments of yeast (Saccharomyces cerevisiae) cell walls to remove mannan and glycogen is still heterogeneous. The major component (about 85%) is a branched beta-(1-->3)-glucan of high molecular weight (about 240000) containing 3% of beta-(1-->6)-glucosidic interchain linkages. The minor component is a branched beta-(1-->6)-glucan. A comparison of our results with those of other workers suggests that different glucan preparations may differ in the degree of heterogeneity and that the major beta-(1-->3)-glucan component may vary considerably in degree of branching.

The fine structure of amylopectin

Abstract A critical examination of an enzymic method for determining the ratio of A and B chains in amylopectin leads to a value of ∼ 1:1, and not 2:1 as suggested other workers. Partial debranching with pullulanase gave results consistent with earlier suggestions that A chains are predominantly and selectively removed. The ratio of A and B chains in a partially branched amylopectin has been determined, and the results are discussed in relation to possible structures for amylopectin.

Isolation and composition of an alkali-soluble glucan from the cell walls of Saccharomyces cerevisiae.

An alkali-soluble glucan was obtained from the cell walls of Saccharomyces cerevisiae NCYC1109 and bakers yeast by extraction with cold, dilute sodium hydroxide under nitrogen. The glucan, which represented approximately 20% of purified glucan was homogeneous and was shown to be free from contamination by other cell-wall polysaccharides by ultracentrifuging, gel filtration and electrophoresis. In addition to glucose, the glucan contained traces of mannose and nitrogen, but no hexosamine. Structural analyses revealed the presence of 80-85% (1 leads to 3)-beta-D linkages, 8-12% (1 leads to 6)-beta-D linkages and 3-4% branched residues linked through C-1, C-3 and C-6. The molecular weight of the glucan was estimated to be about 250000. Electron-microscopic examination of the cell walls after alkali extraction showed that an amorphous surface layer had been removed revealing numerous bud scar structures.

Recent developments in our understanding of glycogen structure

Abstract The main structural features of glycogen were established many years ago by predominantly chemical methods. However, the fine structure continues to be the subject of experimental investigations by enzymic methods. Current topics include: (a) the mechanism of the formation of the linkage between glycogen and protein during the first stages of biosynthesis; (b) the arrangement of the constituent chains to form β-particles of molecular weight ∼ 107; (c) the mode of aggregation of β-particles to form much larger α-particles; and (d) the possible presence of monosaccharide residues other than d -glucose, and of phosphate ester groups. This review comprises a critical discussion of the above and related aspects of glycogen structure.

The molecular structures of some glucans from the cell walls of Schizosaccharomyces pombe

Abstract Extraction of the cell walls of Schizosaccharomyces pombe with dilute alkali at 4° yields a mixture of polysaccharides including galactomannan, (1→3)-α- d -glucan, and a branched (1→3)-β- d -glucan. The alkali-insoluble residue contains a lightly branched (1→3)-β- d -glucan, together with smaller amounts of an extremely highly branched (1→6)-β- d -glucan. The properties of the three distinct β- d -glucans are compared with those isolated from other yeasts.

Structural analysis and ensymic solubilization of barley endosperm cell-walls

Abstract Barley endosperm cell-walls were prepared and analysed. The-carbohydrate portion, which constituted most of the wall material, consisted of 10 % of l -arabinose, 13% Of d -xylose, 74% of d -glucose and 2.5% of d -mannose. Mixed-linkage β- d -glucan represented 70-72% of this material; the remaining 2-4% Of d -glucose maybe present as cellulose and glucomannan. Water and alkali-extracted β- d -glucans contained similar ratios of (1 → 3)- to (1 → 4)-Linkages, namely 3 to 7. The walls, which had a protein content of approximately 5 %, contained unidentfied, alkali-labile linkages. An endo-(1 → 3)β- d -glucanase from malted barley, and a fungal endo-(1 → 4)-β- d -glucanase, caused extensive solubilization of the wall polysaccharides.

The Enzymic Degradation of an Alkali-soluble Glucan from the Cell Walls of Saccharomyces cerevisiae

An alkali-soluble glucan from the cell walls of Saccharomyces cerevisiae NCYC1109 has been hydrolysed with a purified endo-(1 leads to 3)-beta-D-glucanase and an endo-(1 leads to 6)-beta-D-glucanase from Bacillus circulans WL-12. The products of enzyme action include various oligosaccharide and polysaccharide fractions which have been separated by gel filtration and characterized, giving new information on the fine structure of the glucan. The isolated cell walls have also been subjected to enzymic hydrolysis. The results suggest that part of the cell-wall mannan is held in place by a glucan component.

Studies on carbohydrate metabolizing enzymes. XVI. Specificity of laminaribiose phosphorylase from Astasia ocellata.

Abstract Cell-free extracts of the protozoon Astasia ocellata show laminaribiose phosphorylase activity. The enzyme catalyzes the reversible phosphorolysis of laminaribiose (and higher laminarisaccharides) to glucose and α- d -glucose 1-phosphate. At equilibrium, synthesis of laminaribiose is favored. For synthesis, α- d -glucose 1-phosphate is the only known glucosyl donor. Possible acceptor substrates are β- d -glucopyranose and di- or trisaccharides (or derivatives) which contain a nonreducing β- d -glucopyranosyl residue, the transferred glucose residue being attached by a (1 → 3)-linkage. In the presence of arsenate, laminaribiose is completely converted into glucose.

An enzymic method for the determination of the degree of polymerisation of glucans

Abstract The number-average degree of polymerisation of glucans may be determined by measurement of the sorbitol ( D -glucitol) content of an acid hydrolysate of the borohydride-reduced glucan, using sorbitol dehydrogenase. The method is applicable to both linear and branched polymers of either α- or β- D -glucose.