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Evolution of the development of how starch is biosynthesized

Authors

  • John F. Robyt,

    Corresponding author
    1. Laboratory of Carbohydrate Chemistry and Enzymology, The Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA, USA
    • Laboratory of Carbohydrate Chemistry and Enzymology, The Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, 4252 Molecular Biology Bldg., Iowa State University, Ames, IA 50011, USA Fax: +1-515-294-0453.
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  • Rupendra Mukerjea

    1. Laboratory of Carbohydrate Chemistry and Enzymology, The Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA, USA
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Abstract

In 1940, C.S. Hanes found that potato phosphorylase transferred a few two to three glucose units from α-D-Glc-1-P to the nonreducing-ends of starch. Starting with only α-D-Glc-1-P and phosphorylase, there was no reaction and a starch-primer was required for reaction. In 1960, Leloir and coworkers incubated starch granules with ADP-[14C]Glc and found that 14C-starch was synthesized. Reaction with β-amylase gave 14C-maltose from the nonreducing-ends and it was assumed that the glucose was being added to the nonreducing-ends of a primer. Mukerjea and Robyt pulsed and chased starch-granules with ADP-[14C]Glc and ADPGlc, and found on reduction and hydrolysis of the 14C-starch, 14C-D-glucitol was obtained, indicating that glucose was added to the reducing-ends of growing starch-chains. They obtained highly purified, starch-synthase that was shown to be free of starch-primers and gave de novo synthesis, with the addition of glucose to the reducing-ends. They also found 61 papers from 1964 to 2012 that used 50–100 mM Tris-type buffers with starch-synthase and had to add putative-primers to obtain activity. Mukerjea et al. showed that 25 mM Tris-type buffers, completely inhibited starch-synthase. Addition of 10 mg/mL putative-primers, glycogen or maltotetraose, gave partial (8–57%) reversal of the inhibition. The putative-primers were activators and not primers; however, their use perpetuated the primer myth for 50 years. A hypothesis is developed, as to how starch granules are initiated and grow in vivo.

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