Evolution of the development of how starch is biosynthesized

In 1940, C.S. Hanes found that potato phosphorylase transferred a few two to three glucose units from a-D-Glc-1-P to the nonreducing-ends of starch. Starting with only a-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 beta-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 50100?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 (857%) 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.