string: Furthermore, the kinetics of exo-AFBO formation by P450 1A5 followed Michaelis– Menten kinetics (Yip and Coulombe, 2006), while that for 3A37 exhibited sigmoidal kinetics following the Hill equation, suggestive of apparent cooperativity between AFB1 and P450 3A37 (Rawal et al., 2010b).