Cytosolic heteroglycans in photoautotrophic and in heterotrophic plant cells

• Published in: Phytochemistry (Oxford) Vol. 70; no. 6; pp. 696 - 702
• Main Authors: Fettke, Joerg, Malinova, Irina, Eckermann, Nora, Steup, Martin
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Ltd 01.04.2009; Elsevier
• Subjects: Biological and medical sciences; Chemical constitution; cytosol; Cytosol - chemistry; Cytosolic heteroglycans; Cytosolic phosphorylase; Cytosolic transglucosidase; enzyme activity; Fundamental and applied biological sciences. Psychology; glucosyltransferases; glycosidic linkages; glycosyltransferases; heterotrophs; isozymes; literature reviews; Maltose metabolism; monosaccharides; phosphorylase; Plant Cells; Plant physiology and development; Plants - chemistry; polysaccharides; Polysaccharides - chemistry; starch; Starch metabolism; sucrose; Starch metabolism; Cytosolic transglucosidase; Cytosolic phosphorylase; Cytosolic heteroglycans; Maltose metabolism; Enzyme; Starch; Transferases; Glycosyltransferases; Chemical structure; Metabolism; Cytosol; In vitro; Phosphorylase; Plant origin; Hexosyltransferases; Pharmacokinetics
• ISSN: 0031-9422; 1873-3700
• DOI: 10.1016/j.phytochem.2009.03.016

Cytosolic heteroglycans (HG) are essential for the conversion of starch-derived maltose to sucrose or other metabolites. In easily reversible reactions, two glucosyl transferases, the transglucosidase (DPE2) and the phosphorylase isozyme (Pho2/PHS2), utilize HG both as glucosyl donor and acceptor. In plants several ‘starch-related’ enzymes exist as plastid- and cytosol-specific isoforms and in some cases the extraplastidial isoforms represent the majority of the enzyme activity. Due to the compartmentation of the plant cells, these extraplastidial isozymes have no access to the plastidial starch granules and, therefore, their in vivo function remained enigmatic. Recently, cytosolic heteroglycans have been identified that possess a complex pattern of the monomer composition and glycosidic bonds. The glycans act both as acceptors and donors for cytosolic glucosyl transferases. In autotrophic tissues the heteroglycans are essential for the nocturnal starch–sucrose conversion. In this review we summarize the current knowledge of these glycans, their interaction with glucosyl transferases and their possible cellular functions. We include data on the heteroglycans in heterotrophic plant tissues and discuss their role in intracellular carbon fluxes that originate from externally supplied carbohydrates.