Nearly complete backbone resonance assignments for the 357 residue, 42 kDa enzyme arginine kinase in a transition state analogue (TSA) complex are presented. The TSA is a quaternary complex of arginine kinase, MgADP, arginine, and nitrate. About 93% (320 of 344) of the non-proline backbone amides were assigned using an enzyme enriched with (2)H, (13)C, and (15)N in combination with three enzyme samples prepared with a single (15)N-labeled amino acid (K, L, and R). The amide assignments will provide the foundation for investigating the dynamics of arginine kinase when in a TSA complex.