4-CPI

4-CPI (4-(4-Chlorophenyl)imidazole) is a CYP2B4 inhibitor with an IC₅₀ of 0.11 μM and a K_d of 0.043 μM. The K_s of 4-CPI for cytochrome P450eryF (S93C/C154S mutant) is 9.4 μM, with no allosteric cooperative effect of ligand binding^[1][2]. 4-CPI binds to CYP2B4 at a 1:1 ratio, which induces substantial conformational changes in the enzyme's active pocket to form a closed crystal conformation (PDB:1SUO). 4-CPI can be used to investigate the flexibility of P450 active pockets, protein-ligand binding thermodynamics, and the allosteric mechanisms of P450^[1][2]. In Vitro:4-CPI (4-(4-Chlorophenyl)imidazole) (0-30 μM) inhibits the 7-ethoxy-4-trifluoromethylcoumarin oxidation activity of purified 2B4dH (H226Y) with an IC₅₀ of 0.11 μM^[1].
4-CPI (0-2.5 μM) binds to purified 2B4dH (H226Y) with a K_D value of 0.043 μM, and induces type II heme spectral changes at 25 °C^[1].
Binding of 4-CPI (10 μM; 1 hour) to purified 2B4dH (H226Y) reduces the accessibility of Trp¹²¹ to acrylamide by 2-fold, indicating that helix C containing Trp¹²¹ undergoes a conformational change and enters an environment with lower solvent exposure^[1].
4-CPI docks into the experimentally observed binding pocket of the closed crystal structure of 2B4dH (H226Y)^[1].
4-CPI (120 μM) induces dimerization of purified 2B4dH (H226Y) in the absence of CYMAL-5, whereas the protein remains in a monomeric state in the presence of 1 mM CYMAL-5^[1].
4-CPI (0-12 μM) binds to the purified P450eryF (S93C/C154S) mutant at a 1:1 stoichiometric ratio, with a binding constant K_s of 9.4 μM, and induces type II spectral changes^[2].
4-CPI binds to a single high-affinity site near the heme of the P450eryF (S93C/C154S) homology model, with no stable secondary high-affinity binding site, which is consistent with its non-cooperative 1:1 binding behavior^[2].