Selective 1H- 13C NMR spectroscopy of methyl groups in residually protonated samples of large proteins.

Methyl (13)CHD(2) isotopomers of all methyl-containing amino-acids can be observed in residually protonated samples of large proteins obtained from [U-(13)C,(1)H]-glucose/D(2)O-based bacterial media, with sensitivity sufficient for a number of NMR applications. Selective detection of some subsets of methyl groups (Ala(beta), Thr(gamma 2)) is possible using simple 'out-and-back' NMR methodology. Such selective methyl-detected 'out-and-back' NMR experiments allow complete assignments of threonine gamma 2 methyls in residually protonated, [U-(13)C,(1)H]-glucose/D(2)O-derived samples of an 82-kDa enzyme Malate Synthase G. [U-(13)C,(1)H]-glucose/D(2)O-derived protein samples are relatively inexpensive and are usually available at very early stages of any NMR study of high-molecular-weight systems.