Reserve glucans

These polymers are distinguished from cellulose by the presence of both/ -(l— 3)- and / -(l— 4)-linked D-glucosyl residues, lower molecular weights (some noncellulosic glucans are water-soluble), and susceptibility to hydrolysis by / -D-glucanases that cannot hydrolyze cellulose. Unlike cellulose, whose microfibrillar structure and structural role in the cell wall has been clearly established, the function of these polymers as structural components of the wall is still a subject of controversy there is some evidence that they are energy-reserve materials.110-201 202... 

Paulsen BS, Myklestad SM (1978) Structural studies of the reserve glucan produced by the marine diatom Skel-etonema costatum. Carbohydr Res 62 386-388 Peperzak L, Colijn F, Vrieling EG, Gieskes WWC, Peeters JCH (2000) Observations of flagellates in colonies of Phaeocystis globosa (Prymnesiophyceae) a hypothesis for their position in the life cycle. J Plankt Res 22 2181-2203... 

Varum KM, Kvam BJ, Myklestad SM (1986) Structure of a food-reserve beta-D-glucan produced by the hapto-phyte alga Emiliania huxleyi (Lohmann) Hay and Mohler. Carbohydr Res 152 243-248 Veldhuis MJW, Admiraal W (1985) Transfer of photosynthetic products in gelatinous colonies of Phaeocystis pouchetii (Haptophyceae) and its effect on the measurement of excretion rate. Mar Ecol Prog Ser 26 301-304... 

It is not always clear whether cell-wall polysaccharides have a structural or reserve function because some, for example, the /3-glucans of cereal grains, may have dual roles. However, it is likely that the /3-glucans and other hemicelluloses in cell walls of tissues other than those in... 

Glucane provides an exocellular reserve for Botrytis cinerea. Its mobihzation requires a fi-... 

Rapidly growing cultures (Table 2, exp. phase) show PER values from 2 -10 in most cases,but may increase to 10-30 in some cases. Mague et al. [22] concluded that extracellular release is a normal function of healthy cells and showed that the relative composition of Skeletonema costatum cellular and the extracellular fraction of amino acids was quite different. Marlowe et al. [23] fractionated cellular and extracellular material and found a marked difference in the content of ionic compounds in the two fractions. Myklestad et al. [24] found the reserve polysaccharide P-l,3-glucan to be quite dominating in the soluble cellular fraction of Chaetoceros affinis while the extracellular polysaccharide produced was entirely different and contained no glucose at all in the molecule... 

The comparison between the two chain pairs is also consistent with the physical properties. Paramylon and amylose are known for their gel forming properties and their carbon reserve function in p1 ants.(13,69) Although (l- -3)-3-D-glucan also plays a structural rFTe when it occurs in the cell walls of yeast( ), it is probably more of a matrix substance than anything else. The ability to form multiple helices probably accounts for unusual solubility phenomena such as retrogradation( ) and irreversible gel formation on heating. (13)... 

Many red algae (Rhodophyceae) contain complex carbohydrate molecules. These algae produce D-glucans, known as floridean starch, as their food reserve material (Percival,... 

In the Phaeophyceae (brown algae), the food reserves are laminarin, a water-soluble P-D-(l- 3)-linked D-glucan and a sugar alcohol, mannitol. Laminarin contains 20-25 glucose units (Percival, 1970, 1979). 

Hemicelluloses high molecular mass polysaccharides of p-l,4-linked hexose and pentose residues, often also containing uronic acid. H. occur in woody parts of plants together with cellulose, serving as structural compounds and sometimes as reserve substances. They are insoluble in water, but soluble in dilute alkali. Humans and animals cannot digest them. Important H. are arabans, xylans, glucans, galactans, fructans and mannans. 

General term for low M.W. water-soluble reserve glucans from phaephyte algae. Soluble and insoluble forms were earlier recognised, but laminarans differ considerably in struct. 

Starch is a glucan and is present in many plants as a reserve carbohydrate. It is most abundant in seeds, fruits, tubers and roots. Starch occurs naturally in the form of granules, whose size and shape vary in different plants. The granules are built up in concentric layers, and although glucan is the main component of the granules they also contain minor constituents such as protein, fatty acids and phosphorus compounds, which may influence their properties. 

The reserve o-glucan stored by the marine diatom Skeletonema costatum is based on a yS-(l -> 3)-o-glucan backbone with occasional branch points at C-2 and C-6. Although this structure is called a Chrysolaminaran-type , none of the polysaccharide chains were terminated at their reducing end by residues of D-mannitol. The molecular weight of these polymers was 1.3 x 10 with an average chain length of ca. 11 residues. 

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