The isomers eoxin (“ee-OX-in”) A4 and leukotriene (“leuko-TRY-een”) A4 bear this group before it is removed by coupling to glutathione (“gluta-THIGH-own”). Rifampin indirectly increases carbamazepine (“car-buh-MAY-zuh-peen”) activity by promoting the addition of this group, while grapefruit has the opposite effect. Post-translational modification by gamma-glutamyl carboxylase (“carboxy-lase”) adds this group to (10[1])its cofactor, which must be removed by the VKOR (“V-kor”) complex. The addition (10[1])of this group to aflatoxin (“afla-toxin”) enables it to cause liver damage. (10[2]-5[1])The ability (10[1])of PAHs (“P-A-H’s”) to cause (10[1])transitions and transversions is attributed to the addition of this functional group by cytochrome (-5[1])P450s, (10[1])which may be followed by hydrolysis to form a (-5[1])vicinal diol (10[1]-5[1])(“VISS-ih-null DYE-ol”). The C-3 (10[1])hydroxyl (10[1])of sterols derives from one of these functional groups added to a double bond by squalene (10[1])monooxygenase (“mono-oxygen-ace”). For 10 points, name this reactive group consisting of a three-membered (10[1])ether (10[2])ring. (10[3])■END■ (10[5]0[2])