Biosynthesis of L-valine in Salmonella typhimurium: origin of the diastereotopic methyl groups

Abstract

When [1,3,5-13C3]-α-acetolactate {[1,3,5-13C3]-2-hydroxy-2-methyl-3-oxobutanoate}(1′) was incubated with a cell-free system from Salmonella typhimurium, the valine (5′) produced was labelled in the C-4 pro-S position, proving that during the tertiary ketol rearrangement catalysed by the enzyme reductoisomerase, the methyl group transfer is to the re face of the trigonal centre at C-3 of α-acetolactate (1′).