Cytochrome P450 4A11 (CYP4A11) is a fatty acid hydroxylase enzyme expressed in human liver. It catalyzes not only the hydroxylation of saturated and unsaturated fatty acids, but the conversion of arachidonic acid to 20-hydroxyeicosatetraenoic acid (20-HETE), a regulator of blood pressure. In this study, we performed a directed evolution analysis of CYP4A11 using the luminogenic assay system. A random mutant library of CYP4A11, in which mutations were made throughout the entire coding region, was screened with luciferase activity to detect the demethylation of luciferin-4A (2-[6-methoxyquinolin-2-yl]-4,5-dihydrothiazole-4-carboxylic acid) of CYP4A11 mutants in Escherichia coli. Consecutive rounds of random mutagenesis and screening yielded three improved CYP4A11 mutants, CP2600 (A24T/T263A), CP2601 (T263A), and CP2616 (A24T/T263A/V430E) with ~3-fold increase in whole cells and >10-fold increase in purified proteins on the luminescence assay. However, the steady state kinetic analysis for lauric acid hydroxylation showed the significant reductions in enzymatic activities in all three mutants. A mutant, CP2600, showed a 51% decrease in catalytic efficiency (k cat/K m) for lauric acid hydroxylation mainly due to an increase in K m. CP2601 and CP2616 showed much greater reductions (>75%) in the catalytic efficiency due to both a decrease in k cat and an increase in K m. These decreased catalytic activities of CP2601 and CP2616 can be partially attributed to the changes in substrate affinities. These results suggest that the enzymatic activities of CYP4A11 mutants selected from directed evolution using a luminogenic P450 substrate may not demonstrate a direct correlation with the hydroxylation activities of lauric acid.
Animals ; Arachidonic Acid ; Blood Pressure ; Cats ; Clinical Coding ; Cytochrome P-450 Enzyme System ; Escherichia coli ; Fatty Acids, Unsaturated ; Humans* ; Hydroxylation ; Liver ; Luciferases ; Luminescence ; Mass Screening ; Mutagenesis

Abstract: A 16-year-old cat presented with a 2-week history of anorexia and lethargy. Radiography revealed a soft-tissue opacity, heart-shaped mass between the descending colon and urinary bladder. Ultrasonography showed a large uterine body with a heterogeneously hypoechoic, thickened wall and hypoechoic intraluminal fluid. Computed tomography revealed a large, fluid-filled uterine mass with contrast enhancement, without evidence of regional lymph node or pulmonary metastasis. Ovariohysterectomy was performed and leiomyosarcoma was confirmed by histology. No notable abnormalities were observed during the 1-year postoperative follow-up periods. This report describes the diagnostic imaging and treatment of a rare case of feline uterine leiomyosarcoma.

Genomic analysis indicated that the genome of Drosophila melanogaster contains more than 80 cytochrome P450 genes. To date, the enzymatic activity of these P450s has not been extensively studied. Here, the biochemical properties of CYP6A8 were characterized. CYP6A8 was cloned into the pCW vector, and its recombinant enzyme was expressed in Escherichia coli and purified using Ni2+ -nitrilotriacetate affinity chromatography. Its expression level was approximately 130 nmol per liter of culture. Purified CYP6A8 exhibited a low-spin state in the absolute spectra of the ferric forms. Binding titration analysis indicated that lauric acid and capric acid produced type І spectral changes, with Kd values 28 ± 4 and 144 ± 20 μM, respectively. Ultra-performance liquid chromatography–mass spectrometry analysis showed that the oxidation reaction of lauric acid produced (ω-1)-hydroxylated lauric acid as a major product and ω-hydroxy-lauric acid as a minor product. Steady-state kinetic analysis of lauric acid hydroxylation yielded a kcat value of 0.038 ± 0.002 min –1 and a Km value of 10 ± 2 μM. In addition, capric acid hydroxylation of CYP6A8 yielded kinetic parameters with a kcat value of 0.135 ± 0.007 min –1 and a Km value of 21 ± 4 μM. Because of the importance of various lipids as carbon sources, the metabolic analysis of fatty acids using CYP6A8 in this study can provide an understanding of the biochemical roles of P450 enzymes in many insects, including Drosophila melanogaster.