Human liver lauric acid hydroxylase activities.
Nine male and five female human liver microsomal sample were examined for laurate 11- and 12-hydroxylase activities. The mean specific activities for the 11- and 12-hydroxylation reactions were 0.78 +/- 0.33 and 1.07 +/- 0.12 nmol/min/mg protein, respectively. Antibody inhibition experiments, using a polyclonal antibody to a cytochrome P450 (P450) isolated from diethylhexyl phthalate-treated rats, which recognizes forms P4504A1, P4504A2, and P4504A3 of the rate, inhibited the 12-hydroxylase activity by 65%, but did not affect 11-hydroxylase activity. Western-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 support the 12-hydroxylation of lauric acid. Laurate 11-hydroxylase activity was inhibited by diethyldithiocarbamate, an inhibitor of P4502E1-mediated reactions, and by chlorzoxazone, a P4502E1 substrate. A comparison of laurate 11-hydroxylase activities with densitometric values of the P4502E1 protein bands indicated a strong correlation existed (0.82). An analysis of microsomal samples containing expressed human forms P4501A2, P4502A6, P4502C8, P4502C9, P4502D6, P4502E1, and P4503A4 showed that only form P4502E1 supported the 11-hydroxylation reaction.
Castle
P J
PJ
Pharmacology/Toxicology Graduate Program, Washington State University, Pullman 99164-6510, USA.
Merdink
J L
JL
Okita
J R
JR
Wrighton
S A
SA
Okita
R T
RT
D000293:Adolescent; D000328:Adult; D000818:Animals; D019392:Cytochrome P-450 CYP2E1; D042926:Cytochrome P-450 CYP4A; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism* / Q000502:physiology; D005260:Female; D006801:Humans; D006900:Hydroxylation; D007850:Lauric Acids / Q000378:metabolism; D008099:Liver / Q000201:enzymology*; D008297:Male; D008875:Middle Aged; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D010089:Oxidoreductases, N-Demethylating / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley
D007850:Lauric Acids; C030358:lauric acid; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D019392:Cytochrome P-450 CYP2E1; D042926:Cytochrome P-450 CYP4A; D010089:Oxidoreductases, N-Demethylating