Interaction of Cefpiramide sodium with bovine hemoglobin and effect of the coexistent metal ion on the protein-drug association

The interaction between bovine hemoglobin (BHb) and cefpiramide sodium (CPMS) was investigated at different temperatures by fluorescence, UV absorption, and CD spectroscopy, as well as the effect of common metal ions (Mg2+, Zn2+, Cu2+, Co2+, Fe3+, Ni2+) on the BHb-CPMS system. Results showed that CPMS could quench the intrinsic fluorescence of BHb strongly, and the quenching mechanism was a static quenching process. The electrostatic force played an important role on the conjugation reaction between BHb and CPMS. The order of magnitude of binding constants (Ka) was 104, the number of binding site (n) in the binary system was approximately equal to 1 and the binding distance (r) was about 3.08 nm. Besides, the values of Hill's coefficients were approximately equal to 1, which indicated there was almost no cooperativity in CPMS's binding with BHb. Synchronous spectra and CD spectra revealed that the microenvironment and the conformation of BHb were changed during the binding reaction. Studies on the interaction between BHb and drug will facilitate interpretation of the drug's metabolism and transporting process in the blood, and will help to explain the relationship between structures and functions of BHb.