title: Molecular structure of starches from maize mutants deficient in starch synthase III.
abstract: Molecular structures of starches from dull1 maize mutants deficient in starch synthase III (SSIII) with a common genetic background (W64A) were characterized and compared with the wild type. Amylose content with altered structure was higher in the nonwaxy mutants (25.4-30.2%) compared to the wild type maize (21.5%) as revealed by gel permeation chromatography. Superlong chains of the amylopectin component were found in all nonwaxy samples. Unit chain length distribution of amylopectins and their φ,β-limit dextrins (reflecting amylopectin internal structure) from dull1 mutants were also characterized by anion-exchange chromatography after debranching. Deficiency of SSIII led to an increased amount of short chains (DP ≤36 in amylopectin), whereas the content of long chains decreased from 8.4% to between 3.1 and 3.7% in both amylopectin and φ,β-limit dextrins. Moreover, both the external and internal chain lengths decreased, suggesting a difference in their cluster structures. Whereas the molar ratio of A:B-chains was similar in all samples (1.1-1.2), some ratios of chain categories were affected by the absence of SSIII, notably the ratio of "fingerprint" A-chains to "clustered" A-chains. This study highlighted the relationship between SSIII and the internal molecular structure of maize starch.
authors: School of Chemical Sciences, University of Auckland , Private Bag 92019, Auckland 1142, New Zealand.
authors: Fan
authors: F
authors: Zhu
authors: Eric
authors: E
authors: Bertoft
authors: Anna
authors: A
authors: Källman
authors: Alan M
authors: AM
authors: Myers
authors: Koushik
authors: K
authors: Seetharaman
mesh_terms: D015394:Molecular Structure; D009154:Mutation; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D013213:Starch / Q000737:chemistry* / Q000378:metabolism; D013214:Starch Synthase / Q000172:deficiency / Q000235:genetics*; D003313:Zea mays / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics*
chemical_list: D010940:Plant Proteins; D013213:Starch; D013214:Starch Synthase