Electrospray Ionization Mass Spectrometry of Noncovalent or Covalent Binding Complexes of Drugs with Proteins

ESI/MS of the noncovalently and covalently bound complexes of drugs with protein is useful to study on pharmacological effect or toxicological symptom of drugs because of solving the problem with far greater easier by MS than any other method. ESI/MS shows that protein folding of FKBP generates a native three-dimensional structure with multiple charged ions (+6~+8) at pH 6.8 from a denature linear one-dimensional structure with multiple charged ions (+10~+20) at pH 3.0. The noncovalently bound complex of FKBP-FK506 (12.6 kd) is observed a little in mixed solution of FK506 (0.8 kd) and FKBP (11.8 kd) at pH 3 or pH 6.8 by ESI/MS and its deconvoluted MS. But much amount of FKBP-FK506 (12.6 kd) generate during folding of FKBP after the pH of the solution containing FKBP and FK506 changes from pH 3.0 to pH 6.8. Drug A is a large ring compound with aminal bond and produced the covalent complex with human serum albumin (DA=HSA) that was measured easily by LC/ESI/MS and its deconvoluted mass. The stoichiometry of ratio (Drug : HSA) was shown by molecular ions at m/z 67,610 (1:1 DA=HSA complex), 68,792 (2:1 DA=HSA complex), 70,187 (3:1 DA=HSA complex). The main metabolites acyl glucronides of Drug B and C produced the covalent binding complex with HSA (DB=HSA and DC=HSA) that were easily measured by post-averaging scan of LC/ESI/MS and its deconvoluted MS. These data are useful to improve the post candidate and decide stop and continue of development.