title: Potent inhibition of starch-synthase by Tris-type buffers is responsible for the perpetuation of the primer myth for starch biosynthesis.
abstract: 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.
authors.affiliation: Laboratory of Carbohydrate Chemistry and Enzymology, Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA 50011, USA.
authors.forename: Rupendra
authors.initials: R
authors.lastname: Mukerjea
authors.forename: Amanda P
authors.initials: AP
authors.lastname: McIntyre
authors.forename: John F
authors.initials: JF
authors.lastname: Robyt
mesh_terms: D002021:Buffers; D005998:Glycine / Q000031:analogs & derivatives / Q000737:chemistry / Q000494:pharmacology*; D015394:Molecular Structure; D013213:Starch / Q000096:biosynthesis*; D013214:Starch Synthase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013329:Structure-Activity Relationship; D014325:Tromethamine / Q000494:pharmacology*
chemical_list: D002021:Buffers; D014325:Tromethamine; D013213:Starch; D013214:Starch Synthase; D005998:Glycine