SYNTHESIS OF [U-C-13, N-15]-CYSTEINE HYDROCHLORIDE - AN IMPORTANT TOOL FOR HETERONUCLEAR, MULTIDIMENSIONAL NMR-STUDIES OF PROTEINS

Protein structure determination by modern NMR techniques is greatly facilitated using N-15- and C-13-labeled proteins. Labeling of proteins that are overexpressed in mammalian cells is a difficult task that requires a growth medium consisting. of algal hydrolysates supplemented with labeled amino acids. Although most of the amino acids can be obtained to prepare an isotopically labeled growth medium for mammalian cells,[U-C-13,N-15]-cysteine is not available, hampering the backbone and cysteine side-chain assignments and structure determination in the vicinity of the cysteine residues. A synthesis of D,L-[U-C-13,N-15]-cysteine hydrochloride in good overall yield is described which makes use of readily available N-15- and C-13-labeled starting materials and will facilitate heteronuclear multidimensional NMR studies of proteins that are overexpressed in mammalian cells.