Potent inhibition of starch-synthase by Tris-type buffers is responsible for the perpetuation of the primer myth for starch biosynthesis

Mukerjea and Robyt [Carbohydr. Res.2012, 352, 137–142] showed that a primer-free potato starch-synthase synthesized starch chains de novo, without the addition of a primer. A dichotomy arises as to why 61 studies from 1964 to the present have had to add a carbohydrate primer to obtain starch-synthase activity. All of these studies used 25–100 mM Tris, Bicine, or Tricine buffers. We have found that the Tris-type buffers completely inhibit starch-synthase at these concentrations. The addition of 10 mg/mL of the putative primers, glycogen and maltotetraose, gave a partial reversal of the inhibition, with glycogen being better than maltotetraose. It has been found that the Tris-type buffers form a complex with the ADPGlc substrate, removing it from the digest, causing the inhibition. The addition of the putative primers releases some of the ADPGlc from the complex, permitting it to act as a substrate for starch-synthase. The study definitively shows that the need for primers for starch-synthase by many investigators from 1964 to the present has been caused by Tris-type buffer inhibition that was partially reversed by putative primers. This has led to the perpetuation of the primer myth for the biosynthesis of starch chains by starch-synthase.

Starch synthase (SS) uses ADPGlc as a substrate. In glycine buffer, SS biosynthesizes starch chains de novo, without a primer. The Tris-type buffers are potent inhibitors of SS by removing ADPGlc from the digest. Addition of 10 mg/mL glycogen releases some ADPGlc, giving partial reversal of the inhibition. This addition has perpetuated the 72-year primer myth.Figure optionsDownload as PowerPoint slideHighlights
► Primer free starch-synthase synthesizes starch chains de novo, without a primer.
► Tris-type buffers (100–25 mM) completely inhibit starch-synthase.
► Tris-type buffers forming complexes with the ADPGlc substrate produced inhibition.
► Adding 10 mg/mL glycogen or maltotetraose putative primers partially reversed the inhibition.
► Partial reversal of the inhibition was produced by the release of ADPGlc from the Tris complexes.