A detailed understanding of molecular recognition is predicated not only on high-resolution static structures of the free and bound states but also on information about how these structures change with time, that is, molecular dynamics. Here we present a deuterium ((2)H) and carbon ((13)C) NMR relaxation study of methyl side chain dynamics in the 82 kDa enzyme malate synthase G (MSG) that is a promising target for the development of new antibiotic agents. It is shown that excellent agreement between (2)H- and (13)C-derived measures of dynamics is obtained, with correlation coefficients exceeding 0.95. The binding interface formed by MSG and its substrates is found to be highly dynamic in the ligand-free state of the enzyme with rigidification upon binding substrate. This study establishes that detailed, quantitative information about methyl side chain dynamics can be obtained by NMR on proteins with molecular masses on the order of 100 kDa and opens up the possibilities for studies of motion in a large number of important systems.