In vitro conversion of leucine to valine: configurational assignment of [5-13C]leucines

• Published in: Biochemistry (Easton) Vol. 20; no. 19; pp. 5609 - 5611
• Main Authors: Sylvester, Steven R, Lan, Suey Y, Stevens, Carl M
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 15.09.1981
• Subjects: Carbon Isotopes; Escherichia coli - metabolism; Isomerism; Lactates - metabolism; Leucine - metabolism; Molecular Conformation; Valine - biosynthesis; Valine - chemical synthesis
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi00522a039

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.