Fruits Produce Branched-Chain Esters Primarily from Newly Synthesized Precursors
Philip Engelgau, Sumithra K. Wendakoon, Nobuko Sugimoto, Randolph M. Beaudry
Abstract
High Resolution Image Download MS PowerPoint Slide Inhibitors of acetohydroxyacid synthase (also known as acetolactate synthase), the common enzyme of branched-chain amino acid biosynthesis, were used as tools to discern the contribution of newly synthesized precursors (i.e., branched-chain amino acids and α-ketoacids) to branched-chain ester formation in ripening apple ( Malus × domestica Borkh.), banana ( Musa spp.), and flowering quince ( Chaenomeles × superba ) fruits. After treatment, anteiso - and iso -branched-chain esters (i.e., those related to isoleucine, and valine and leucine, respectively) universally decreased in content by at least 90%. Among free amino acids, only the branched-chain amino acids, with correspondingly reduced branched-chain esters, had a lesser concentration following treatment with the inhibitor. Branched-chain ester production recovered after subsequent feeding with precursor compounds. Our results ultimately reject the hypothesis that anteiso - and iso -branched-chain esters of ripening fruits are primarily derived from preexisting sources and instead support the hypothesis that these esters are largely the product of de novo precursor biosynthesis.