15-Ketoprostaglandin delta 13-reductase activity in bovine ocular tissues

Purification, cDNA cloning and expression of 15-oxoprostaglandin 13-reductase from pig lung

15-Oxoprostaglandin 13-reductase (PGR) has been purified to apparent homogeneity from pig lung. The enzyme was estimated to have a molecular mass of 36 kDa by both SDS/PAGE and non-denaturing PAGE, indicating that the enzyme is a monomer. 15-Oxo-PGE1, 15-oxo-PGE2 and 15-oxo-PGF2alpha were found to be substrates for the enzyme, whereas the corresponding 15-hydroxyprostaglandins were not. The reverse reaction, the oxidation of 13,14-dihydro-15-oxo-PGE1 to 15-oxo-PGE1, was not observed. Either NADH or NADPH could serve as a coenzyme. However, the Vmax with NADH was approx. 3-fold that with NADPH, while the Km for NADPH was approx. one-tenth that for NADH. Cloning of the cDNA was achieved by PCR and library screening. A 600 bp PCR product containing the sequences of three different tryptic peptides derived from purified PGR was used for cDNA library screening by plaque hybridization. A cDNA clone that contained the entire PGR coding sequence of 987 bp was obtained. The sequence codes for a protein of 329 amino acid residues with a calculated molecular mass of 35791 Da. Homology analysis indicated that the sequence is virtually identical with that of leukotriene B4 (LTB4) 12-hydroxydehydrogenase [Yokomizo, Ogawa, Uozumi, Kume, Izumi and Shimizu (1996) J. Biol. Chem. 271, 2844-2850]. Expression of this cDNA in Escherichia coli resulted in a protein exhibiting both PGR and LTB4 12-hydroxydehydrogenase activities. However, the specific activity of PGR with 15-oxo-PGE1 as a substrate was approx. 300-fold that of LTB4 12-hydroxydehydrogenase. These results indicate that the cloned cDNA codes for a protein with two different enzyme activities, with 15-oxoprostaglandins as the preferred substrates.

Purification and characterization of alpha,beta-ketoalkene double bond reductases from bovine eyes

PURPOSE

To explore the alpha,beta-ketoalkene double bond reductases responsible for xenobiotic metabolism in bovine ocular tissues using trans-phenyl-l-propenyl ketone as a model substrate.

METHODS

A mixture of trans-phenyl-l-propenyl ketone, NADPH or NADH, and an enzyme source in 0.1 M K,Na-phosphate buffer (pH 7.4) was incubated for 15 min at 37 degrees C. Phenyl propyl ketone formed was quantified by high performance liquid chromatography (HPLC).

RESULTS

The lens, ciliary body, iris, retinal pigment epithelium (RPE)-choroid, retina, and cornea exhibited alpha,beta-ketoalkene double bond reductase activities in the presence of NADPH or NADH. An alpha,beta-ketoalkene double bond reductase was purified to homogeneity from the iris-ciliary body cytosol. The molecular weight was estimated to be 58,000 by gel filtration, and 40,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The enzyme activity was inhibited by dicumarol, quercitrin, indomethacin, disulfiram, and p-chloromercuribenzoic acid. The enzyme exhibited double bond reductase activity toward 2-alkenals as well as alpha,beta-ketoalkenes. Another alpha,beta-ketoalkene double bond reductase was also purified to homogeneity from the lens cytosol. The molecular weight was estimated to be 105,000 by gel filtration and 40,000 by SDS-PAGE. The enzyme activity was inhibited by dicumarol and quercitrin. The enzyme exhibited double bond reductase activity toward some alpha,beta-ketoalkenes.

CONCLUSIONS

Two kinds of enzymes responsible for reduction of the carbon-carbon double bond of xenobiotics were purified for the first time from ocular tissues. The molecular weights, substrate specificities, and sensitivities to inhibitors of the enzymes were different from each other.