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From Glycogen to Amylopectin: A Model for the Biogenesis of the Plant Starch Granule

1996; Cell Press; Volume: 86; Issue: 3 Linguagem: Inglês

10.1016/s0092-8674(00)80107-5

1097-4172

Steven Ball, Hanping Guan, Martha G. James, Alan M. Myers, Peter L. Keeling, Grégory Mouille, Alain Buléon, Paul Colonna, J. Preiss,

Biofuel production and bioconversion

Starch constitutes the major source of calories in the human diet. Over 600 commercial products are generated from starch both for food and also non-food uses. Plant Starch can be distinguished from glycogen by the presence of a highly ordered and dense packing of glucan chains. This packing results in the growth of large insoluble granules in the plastids of the eukaryotic plant cell. The enzymes that have been described in the starch biosynthetic pathway are related to those that are involved in cyanobacterial glycogen synthesis. The genetic, molecular biological, and enzymological studies performed to date while allowing constant progress to be made have failed to uncover the biochemical reactions responsible for the synthesis of an ordered crystalline starch structure instead of glycogen. We believe that the order-generating steps have just been discovered in Chlamydomonas and maize. After briefly reviewing our current understanding of amylopectin structure and synthesis, we will present a model that explains the biogenesis of the plant starch granule. This model is consistent with the two-dimensional structures published for the amylopectin clusters, and it is sufficiently predictive to allow us to think in terms of the three dimensional pattern of granule growth.