HUMAN LIVER LAURIC ACID HYDROXYLASE-ACTIVITIES

Nine male and five female human liver microsomal samples were examined for laurate 11- and 12-hydroxylase activities, The mean specific acti vities for the 11- and 12-hydroxylation reactions were 0.78 +/- 0.33 a nd 1.07 +/- 0.12 nmol/min/mg protein, respectively. Antibody inhibitio n experiments, using a polyclonal antibody to a cytochrome P450 (P450) isolated from diethylhexyl phthalate-treated rats, which recognizes f orms P4504A1, P4504A2, and P4504A3 of the rat, inhibited the 12-hydrox ylase activity by 65%, but did not affect 11-hydroxylase activity. Wes tern-blot analyses of the 14 human liver microsomal samples identified one major protein band at 52 kDa that comigrated with human form 4A11 . A correlation coefficient of only 0.19 was calculated when comparing laurate 12-hydroxylase activities and the densitometric values of the immunochemically reactive protein bands in the human liver microsomal samples; which strongly suggests that additional P450 forms also supp ort the 12-hydroxylation of lauric acid. Laurate 11-hydroxylase activi ty was inhibited by diethyldithiocarbamate, an inhibitor of P4502E1-me diated reactions, and by chlorzoxazone, a P4502E1 substrate. A compari son of laurate 11-hydroxylase activities with the densitometric values of the P4502E1 protein bands indicated a strong correlation existed ( 0.82). An analysis of microsomal samples containing expressed human fo rms P4501A2, P4502A6, P4502C8, P4502C9, P4502D6, P4502E1, and P4503A4 showed that only form P4502E1 supported the 11-hydroxylation reaction.