In vitro conversion of leucine to valine: configurational assignment of [5-13C]leucines.
Chiral (2S)-[5-13C]leucine was obtained from Escherichia coli deficient in the synthesis of acetolactate when cultures were supplemented with (RS)-[2-13CH3]acetolactate. The carbon-13 nuclear magnetic resonance spectrum showed one strong peak with a chemical shift of 21.4 ppm relative to tetramethylsilane [Sylvester, S. R., & Stevens, C. M. (1979) Biochemistry 18, 4529-4531]. Silver picolinate oxidation of the labeled leucine gave isovaleric acid which was then brominated at the alpha position to give (2RS)-2-bromo[3-13CH3]-isovaleric acid (2-bromo-3-[13C]methylbutanoic acid). Aminolysis afforded (2RS)-[4-13C]valine which was treated with D-amino acid oxidase in the presence of catalase. The final product was identified as (2S,3S)-[4-13C]valine by the specificity of D-amino acid oxidase, by amino acid analysis, and by the persistence of a strong signal at gamma 17.8 in the carbon-13 magnetic resonance spectrum. These results establish the absolute configuration of the biosynthetic leucine to be (2S,4S)-[5-13C]leucine.
D002247:Carbon Isotopes; D004926:Escherichia coli / Q000378:metabolism*; D007536:Isomerism; D007773:Lactates / Q000378:metabolism; D007930:Leucine / Q000378:metabolism*; D008968:Molecular Conformation; D014633:Valine / Q000096:biosynthesis* / Q000138:chemical synthesis
D002247:Carbon Isotopes; D007773:Lactates; C006359:alpha-acetolactate; D007930:Leucine; D014633:Valine