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In Vitro Synthesis of Ten Starches by Potato Starch-Synthase and Starch- Branching-Enzyme Giving Different Ratios of Amylopectin and Amylose

Mukerjea R, Sheets RL, Gray AN and Robyt JF

The objectives of this study was the use of two highly purified enzymes, potato Starch-Synthase (SS) and Starch- Branching-Enzyme (SBE) to obtain in vitro the syntheses of ten starches, with different ratios of amylopectin and amylose. The amylose was first synthesized by the reaction of SS with ADP [14C] Glc to give ten identical amyloses; the amylopectin was then synthesized by the action of SBE to give ten starches with different amounts of amylopectin. Two of the 14C-amyloses were reacted with 1.0 mIU of purified Starch-Branching-Enzyme (SBE) for 75 and 130 sec, respectively. In a second synthesis, 3 of the amyloses were autoclaved and reacted with 1.0 mIU for 15, 45, and 75 sec. In the third synthesis, 5 amyloses were reacted with different amounts of SBE from 0.50 to 0.01 mIU for 130 sec each. The 10 synthesized starches were separated into amylopectin and amylose fractions. The amylopectin and amylose ratios ranged from 99.9% amylopectin and 0.1% amylose to 10% amylopectin and 90% amylose. The results show that 10 different starches were synthesized, using only two enzymes, SS and SBE. No primers were involved. Glycogen and debranching enzymes were also not involved.