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At least 91 records · Page 5Linked to original sources
PubMed1991

Characteristics of peroxisome proliferation: co-induction of peroxisomal fatty acid oxidation-related enzymes with microsomal laurate hydroxylase.

The profile of the changes in the peroxisomal fatty acid oxidation activity in rat liver was compared with that in microsomal omega-oxidation under various conditions such as a 2-week administration of phenoxyacetic acid derivatives and perfluorinated compounds, short and long-term administration of clofibrate and bezafibrate, high-fat diet feeding, starvation and diabetes. The results were summarized as follows: 1) when phenoxyacetic acid derivatives and perfluorinated compounds were administered, there was a significant correlation in the increase of the activities between peroxisomal fatty acid oxidation and microsomal omega-oxidation. 2) On the long-term administration (79 weeks) of peroxisome proliferators the activities of the enzymes were significantly reduced, but the levels were still higher than the control level in a similar manner. 3) On high-fat diet feeding the patterns of the changes in the activities of peroxisomal fatty acid oxidation, carnitine acetyltransferase and microsomal omega-oxidation were similar to each other, differing from the changes in the activities of microsomal aminopyrin demethylase and mitochondrial carnitine palmitoyltransferase. 4) Under starved and diabetic conditions, co-induction of peroxisomal fatty acid oxidation and microsomal omega-oxidation was observed. From these results it is suggested that 1) the biosynthesis of these enzymes would be regulated on the gene expression of the nearby domain and 2) peroxisomal fatty acid oxidation and microsomal omega-oxidation were co-operatively regulated in order to achieve fatty acid metabolism smoothly.

Animals↗
PubMed1989

Two forms of omega-hydroxylase toward prostaglandin A and laurate. cDNA cloning and their expression.

We have isolated cDNA clones for two forms of P-450s, P-450ka-1 and P-450ka-2, from a rabbit kidney cDNA library, using the cDNA for rabbit pulmonary cytochrome P-450p-2, a prostaglandin omega-hydroxylase (Matsubara, S., Yamamoto, S., Sogawa, K., Yokotani, N., Fujii-Kuriyama, Y., Haniu, M., Shively, J.E., Gotoh, O., Kusunose, E., and Kusunose, M. (1987) J. Biol. Chem. 262, 13366-13371), as a hybridization probe. The cDNAs for P-450ka-1 and P-450ka-2 encode polypeptides of 510 and 511 amino acids, respectively, with sequence similarity of 85% and 87% to P-450p-2. The two deduced primary structures have 87% identity. RNA blot analysis demonstrated that the mRNAs for P-450ka-1 and P-450ka-2 formed single bands at approximately 3.0- and 2.6-kilobase positions, respectively. The mRNA for P-450ka-1 was expressed only in the liver and kidney and was increased remarkably in these tissues by the administration of clofibrate. In contrast, the mRNA for P-450ka-2 was expressed constitutively in the liver, kidney, and small intestine, but its transcription was enhanced only in the liver by clofibrate treatment. Thus, in spite of their high sequence similarity, these P-450 species have different modes of regulatory expression. Comparison of the nucleotide sequences among P-450ka-1, P-450ka-2, and P-450p-2 shows about 90% overall sequence similarity in any pair of the three sequences. Nucleotide replacements are not evenly distributed, but are rather biased. There is a region of approximately 500 base pairs of exceptionally high homology among the three sequences. These results indicate that the gene conversion event occurred during the evolutionary process of these genes.

Amino Acid Sequence↗
PubMed1996

Identification of CYP4A11 as the major lauric acid omega-hydroxylase in human liver microsomes.

Human liver microsomes are capable of oxidizing lauric acid (laurate), a model medium-chain fatty acid, at both the omega- and omega-1 positions to form 12- and 11-hydroxylaurate, respectively. These laurate hydroxylation reactions are apparently catalyzed by distinct P450 enzymes. While the P450 responsible for microsomal laurate omega-1 hydroxylation in human liver has been identified as CYP2E1, the enzyme catalyzing omega-hydroxylation remains poorly defined. To that end, we employed conventional purification and immunochemical techniques to characterize the major hepatic laurate omega-hydroxylase in humans. Western blotting with rat CYP4A1 antibodies was used to monitor a cross-reactive P450 protein (M(r) = 52 kDa) during its isolation from human liver microsomes. The purified enzyme (7.4 nmol P450/mg protein) had an NH2-terminal amino acid sequence identical to that predicted from the human CYP4A11 cDNA over the first 20 residues found. Upon reconstitution with P450 reductase and cytochrome b5, CYP4A11 proved to be a potent laurate omega-hydroxylase, exhibiting a turnover rate of 45.7 nmol 12-hydroxylaurate formed/min/nmol P450 (12-fold greater than intact microsomes), while catalyzing the omega-1 hydroxylation reaction at much lower rates (5.4 nmol 11-hydroxylaurate formed/min/nmol P450). Analysis of the laurate omega-hydroxylation reaction in human liver microsomes revealed kinetic parameters (a lone Km of 48.9 microM with a VMAX of 3.72 nmol 12-hydroxylaurate formed/min/nmol P450) consistent with catalysis by CYP4A11. In fact, incubation of human liver microsomes with antibodies raised to CYP4A11 resulted in nearly 85% inhibition of laurate omega-hydroxylase activity while omega-1 hydroxylase activity remained unaffected. Furthermore, a strong correlation (r = 0.89; P < 0.001) was found between immunochemically determined CYP4A11 content and laurate omega-hydroxylase activity in liver samples from 11 different subjects. From the foregoing, it appears that CYP4A11 is the principle laurate omega-hydroxylating enzyme expressed in human liver.

Animals↗