Effect of isoleusine 208 on nicotine 5′-hydroxylation by human CYP2A6

AIM: To identify potential amino acid residues that contribute to different catalytic characteristics of CYP2A6 and CYP2A13 enzymes in nicotine metabolism. METHODS: Wild type of CYP2A6 and CYP2A13 and their mutants CYP2A6V117A, CYP2A6G164H, CYP2A6I208S, CYP2A6R372H, CYP2A6S465P and CYP2ABA117V, CYP2A13H164G, CYP2A13S208I, CYP2A13H372A and CYP2A13P465S, were subjected kinetic analysis in nicotine 5′-hydroxylation. RESULTS: For CYP2A6, substitution of isoleucine 208 to serine caused dramatic kinetic property changes with K_m and V_max varied from 62.25 μmol•L^-1 and 6. 53 mol•min^-1 •mol ^-1 to 345 μmol•L^-1 and 2. 19 mol•min ^-1 •mol^-1 . However, the corresponding serine 208 to isoleucine mutation did not heavily affect the enzyme activity in CYP2A13. The histidine 372 to arginine mutation resulted in a remarkable catalytic efficiency decrease with K_m and V_max changes from 26. O1 μmol•L^-1 and 24. 51 mol• min^-1•mol ^-1 to 148.7 μmol•L^-1 and 6.11 mol• min ^-1 •mol^-1 in CYP2A13, but the switching of argenine 372 to histidine did not show expected corresponding crucial influence in CYP2A6 activity. Substitutions on the other positions changed enzyme activities in different rates. CONCLUSION: The isoleucine 208 is crucial to human CYP2A6, while the 372 histidine is a key amino acid residue for CYP2A13 in nicotine 5′-hydroxylation.