Prostaglandin 9-ketoreductase and type II 15-hydroxyprostaglandin dehydrogenase from swine kidney are alternate activities of a single enzyme protein

Prostaglandin catabolizing enzymes

The primary catabolic pathway of prostaglandins and related eicosanoids is initiated by the oxidation of 15(S)-hydroxyl group catalyzed by NAD+-dependent 15-hydroxyprostaglandin dehydrogenase (15-PGDH) followed by the reduction of delta13 double bond catalyzed by NADPH/NADH dependent delta13-15-ketoprostaglandin reductase (13-PGR). 13-PGR was also found to exhibit NADP+-dependent leukotriene B4 12-hydroxydehydrogenase (12-LTB4DH) activity. These enzymes are considered to be the key enzymes responsible for biological inactivation of prostaglandins and related eicosanoids. A separate catabolic pathway of thromboxane involves the oxidation of thromboxane B2 (TXB2) at C-11 catalyzed by NAD+-dependent 11-hydroxythromboxane B2 dehydrogenase (11-TXB2DH). The product of this reaction, 11-dehydro-TXB2, has been considered to be a more reliable quantitative index of thromboxane formation in the circulation. Recent biochemical and molecular biological studies have revealed interesting catalytic properties, structure, and activity relationship, and regulation of gene expression of these three enzymes. Future investigation may shed more light on the roles of these enzymes in health and diseases.

Prostaglandin E(2) 9-keto reductase activity in bovine retained and not retained placenta

Prostaglandin E(2) 9-keto reductase (9-KPR) activity shifts reversibly PGE(2) into PGF(2 alpha) and may be responsible for the control of prostaglandins (PGs) levels in, among others, placental tissues. The retention of fetal membranes in cows is the postpartum disorder where the disturbances in PGs metabolism have been reported. It has been argued whether these disturbances are due to alterations in 9-KPR activity. In this study, the activity of the enzyme was determined in maternal and fetal bovine placental tissues which were divided into 6 groups as follows: (A) caesarian section before term without retained fetal membranes (n=10), (B) caesarian section before term with retained fetal membranes (n=10), (C) caesarian section at term without retained fetal membranes (n=12), (D) caesarian section at term with retained fetal membranes (n=12), (E) spontaneous delivery at term without retained fetal membranes (n=12), (F) spontaneous delivery at term with retained fetal membranes (n=12). The enzyme activity was measured spectrophotometrically and expressed in nanokatals (nkat) per protein content. The activity increased towards parturition and was significantly higher in maternal than in fetal part of placenta in all groups examined. The significantly higher values in retained than in not retained placental tissues were observed in the samples examined. The present results indicate that the disturbances in 9-KPR activity in bovine retained placenta exist but their reasons still require further experiments.

Prostaglandin E2 9-keto reductase from bovine term placenta

The aim of the following study was to determine the activity and physico-chemical properties of prostaglandin E2 9-keto reductase from bovine placenta. Placental tissues obtained immediately after parturition were subjected to purification procedure consisting of homogenization, affinity chromatography, gel filtration and allowed to electrophoresis. The activity of enzyme was measured spectrophotometrically. The purification procedures receive 135-fold purified enzyme preparate of the molecular weight of 45 kDa with the following kinetic values: Michaelis constant for PGE2, 117 microM and max velocity 183 pmol/min. The activity of enzyme was also detected with 20 alpha-hydroxypregn-4en-3-one and with 9,10-phenanthrenquinone (Michaelis constant 22 microM and 6 microM, respectively). The determination of physico-chemical properties of prostaglandin E2 9-keto reductase, performed for the first time in bovine placenta, should aid the understanding of the metabolism of prostaglandins and their biological importance in physiological and pathological conditions in cattle.

Heterologous expression of carbonyl reductase: demonstration of prostaglandin 9-ketoreductase activity and paraquat resistance

Transfection of murine NIH3T3 fibroblasts with a pSV2-derived eukaryotic expression vector for human cytosolic carbonyl reductase (E.C. 1.1.1.141) resulted in clones with increased carbonyl reductase activity as demonstrated by an elevation in cellular NADPH-dependent alcohol (menadione) reductase activity. Prostaglandin 9-ketoreductase (9KR) activity, previously noted only in purified enzyme preparations, was also elevated. Although the cellular molar capacity of 9KR activity was less than menadione reductase activity (picomoles versus nanomoles per mg of protein), when compared to endogenous activity there was a greater relative increase in 9KR activity as compared to menadione activity (10 fold increase versus 3 fold). Thus, the 9KR properties of carbonyl reductase may have a physiologic role in prostaglandin regulation. Most transgenic clones lost their enhanced carbonyl reductase activity despite continuous selection, but two clones retained enhanced enzyme activity. RNA analysis indicated that these two murine clones expressed human carbonyl reductase mRNA. These two clones overexpressing carbonyl reductase did not display resistance to menadione, in agreement with a previous report. There was, however, a demonstrable increase in resistance to paraquat of a magnitude similar to that previously noted with transgenic cell lines overexpressing manganese superoxide dismutase.

Suppression of a signaling defect during Myxococcus xanthus development

The csgA gene encodes an extracellular protein that is essential for cell-cell communication (C-signaling) during fruiting body development of Myxococcus xanthus. Two transposon insertions in the socABC operon, soc-560 and socC559, restore development to csgA null mutants. Mixing soc-560 csgA cells or socC559 csgA cells with csgA cells at a ratio of 1:1 stimulated the development of csgA cells, suggesting that soc mutations allow cells to produce the C-signal or a similar molecule via a csgA-independent mechanism. The socABC operon contains the following three genes: socA, a member of the short-chain alcohol dehydrogenase gene family; socB, a gene encoding a putative membrane anchoring protein; and socC, a negative autoregulator of socABC operon expression. Both suppressor mutations inactivate socC, leading to a 30- to 100-fold increase in socA transcription; socA expression in suppressor strains is at least 100-fold higher than csgA expression during all stages of development. The amino acid sequence of SocA has 28% identity and 51% similarity with that of CsgA. We suggest that CsgA suppression is due to overproduction of SocA, which can substitute for CsgA. These results raise the possibility that a cell surface dehydrogenase plays a role in C-signaling.

15-Hydroxyprostaglandin dehydrogenase

Relatively little is known about how 15-PGDH activity is regulated. Changes in 15-PGDH activity have been reported in response to physiological changes brought about by aging, pregnancy, hormonal changes, hypertension and smoking. In addition a large number of drugs have been shown to affect 15-PGDH activity both in vivo and in vitro. The availability of the 15-PGDH cDNA will be a valuable tool for studying how this enzyme is regulated. Isolation of the genomic DNA with its promoter regions has not yet been reported.

Carboxyethyllysine in a protein: native carbonyl reductase/NADP(+)-dependent prostaglandin dehydrogenase

Two different forms of the monomeric NADP(+)-linked prostaglandin dehydrogenase/carbonyl reductase were purified from human placenta and shown to differ by the modification of a lysine residue. The modified and the unmodified proteins were reproducibly recovered in a ratio of approximately 1:3, and both were chemically stable. The modified form was more acidic (pI approximately 7.4 versus pI approximately 7.7) but indistinguishable from the unmodified form in specificity and activity. Amino acid analysis, sequence analysis, mass spectrometry, and chemical synthesis identified the modified residue as N6-(1-carboxyethyl)lysine with C-2 of propionic acid attached to the side-chain N of Lys-238. This compound can be formed from the lysine residue and pyruvate via a Schiff base and subsequent reduction. The enzyme and its NAD(+)-dependent counterpart are distantly related (23% residue identity) and have the same family assignment to short-chain dehydrogenases. Alignments and model-building into the tertiary structure of 3 alpha/20 beta-hydroxysteroid dehydrogenase show that carbonyl reductase has an extra loop (positions 149-189) that forms a separate extension and replaces a backbone C-terminal beta-strand. This change affects the substrate pocket, explaining the different substrate specificities but conserves residues of known functional importance. Carboxyethyllysine at position 238 corresponds to a proteolysis-sensitive position in several short-chain dehydrogenases, less well-defined in the model but close to a surface, and is compatible with the accessibility and enzyme properties observed.

Purification and properties of prostaglandin 9-ketoreductase from pig and human kidney. Identity with human carbonyl reductase

Prostaglandin 9-ketoreductase (PG-9-KR) was purified from pig kidney to homogeneity, as judged by SDS/PAGE using an improved procedure. The enzyme is pro-S stereoselective with regard to hydrogen transfer from NADPH with prostaglandin E2 as substrate and reduces its 9-keto group with approximately 90% stereoselectivity to form prostaglandin F2 alpha. Approximately 8% of the prostaglandin F formed has the beta-configuration. In addition to catalyzing the interconversion of prostaglandin E2 to F2 alpha, PG-9-KR also oxidizes prostaglandin E2, F2 alpha and D2 to their corresponding, biologically inactive, 15-keto metabolites. Incubation of PG-9-KR with prostaglandin F2 alpha and NAD+ leads to the preferential formation of 15-keto prostaglandin F2 alpha rather than prostaglandin E2. This suggests that the prostaglandin E2/prostaglandin F2 alpha ratio is not determined by the NADP+/NADPH redox couple. The enzyme also reduces various other carbonyl compounds (e.g. 9,10-phenanthrenequinone) with high efficiency. The catalytic properties measured for PG-9-KR suggest that its in vivo function is unlikely to be to catalyze formation of prostaglandin F2 alpha. The monomeric enzyme has a molecular mass of 32 kDa and exists as four isoforms, as judged by isoelectric focusing. PG-9-KR contains 1.9 mol Zn2+/mol enzyme and no other cofactors. Human kidney PG-9-KR was also purified to homogeneity. The human enzyme has a molecular mass of 34 kDa and also exists as four isoforms. Polyclonal antibodies raised against pig kidney PG-9-KR cross-react with human kidney PG-9-KR and also with human brain carbonyl reductase, as demonstrated by Western blot analysis. Sequence data of tryptic peptides from pig kidney PG-9-KR show greater than 90% identity with human placenta carbonyl reductase. From comparison of several properties (catalytical, structural and immunological properties), it is concluded that PG-9-KR and carbonyl reductase are identical enzymes.

Effects of saturated fatty acids on prostaglandin E 9-keto-reductase

We examined the effects of three saturated fatty acids (myristic acid 14:0, palmitic acid 16:0, and stearic acid 18:0) on prostaglandin E 9-ketoreductase (PGE-9-KR, EC 1.1.1.189), which catalyzes the conversion of prostaglandin E2 (PGE2) into prostaglandin F2 alpha (PGF2 alpha). Palmitic acid inhibited PGE-9-KR activity dose-dependently, whereas the other two fatty acids had no effect. In spite of the structural similarity of these fatty acids, our findings suggest that, of the three, only palmitic acid has an inhibitory effect on PGE-9-KR.

Purification and characterization of NAD(+)-dependent 15-hydroxyprostaglandin dehydrogenase from porcine kidney

A NAD(+)-dependent 15-hydroxyprostaglandin dehydrogenase (15-OH-PGDH) from porcine kidney was purified to homogeneity by acid precipitation, blue agarose affinity chromatography, hydroxyapatite-ultrogel adsorption chromatography, DEAE-Sephadex ion-exchange chromatography and NAD(+)-agarose affinity chromatography. The specific activity of the homogeneous enzyme was 31.2 U/mg. The molecular mass of the native enzyme was estimated to be 55,000 Da, whereas that of SDS-treated enzyme was 29,000 Da indicating that the native enzyme was dimeric. Compared to human placental 15-OH-PGDH, porcine kidney enzyme gave a similar general amino acid residue distribution. Chemical modification of the enzyme with N-ethyl maleimide (3 microM), N-chlorosuccinimide (20 microM) or 2,4,6-trinitrobenzenesulfonic acid (2.5 microM) followed pseudo-first-order inactivation kinetics, and inactivation could be prevented by the presence of NAD+ (1 mM) but not of prostaglandin E1 (140 microM) indicating the involvement of cysteine, methionine and lysine residues in the coenzyme binding site. Inactivation by diethyl pyrocarbonate (1.25 mM) or phenylglyoxal (10 mM) also showed pseudo-first-order kinetics suggesting that histidine and arginine residues were catalytically or structurally important in the native enzyme. These studies provide new insights into the structure and function of 15-OH-PGDH.

Prostaglandin-E2 9-ketoreductase from swine kidney. Production of antisera and application to development of a radioimmunoassay

Prostaglandin-E2 9-ketoreductase (PGE2-9-KR, EC 1.1.1.189), the enzyme which catalyzes the reaction from prostaglandin E2 (PGE2) to prostaglandin F2 alpha (PGF2 alpha), was purified 580-fold from swine kidney. The molecular mass of the enzyme determined by SDS-gel electrophoresis was 33 kDa. Antiserum against the purified enzyme was raised in three rabbits. The antiserum was able to precipitate PGE2-9-KR from swine kidney and to crossreact with pGE2-9-KR from several reproductive organ tissues, such as rabbit ovary, rabbit corpus luteum, rabbit endometrium and human decidua vera. When swine kidney PGE2-9-KR was labelled with 125I and incubated with affinity-purified antiserum in the presence of increasing amounts of unlabelled enzyme, competitive binding of the unlabelled enzyme to the antibody was observed. A radioimmunoassay for the quantitation of the enzyme was developed. The standard curve was linear from 5 to 500 ng enzyme. The intra- and interassay coefficients of variation were 6.4 and 13.2%, respectively. The assay may be useful for the quantitation of PGE2-9-KR in several tissues under various physiological conditions.

Organ selective conversion of prostaglandin D2 to 9 alpha, 11 beta-prostaglandin F2 and its subsequent metabolism in rat, rabbit and guinea pig

Cell-free 100,000 g supernatants from liver, kidney, lung and caecum of rat, rabbit and guinea-pig were compared for their ability to transform prostaglandins F2 alpha, D2, E2 and 9 alpha, 11 beta-prostaglandin F2 (11epi-PGF 2 alpha) to metabolic products. Experiments utilized multitritiated substrate PGs, with assessment of biotransformation by TLC, HPLC and GC/MS. PGF2 alpha was converted via the sulphasalazine analogue-inhibitable NAD+-dependent 15-hydroxy-prostaglandin dehydrogenase pathway (15-PGDH), with high activity (greater than 5 pmol/min/mg protein) in all 12 systems except rat and rabbit liver (e.g. guinea-pig kidney and rat caecum both 64 pmol/min/mg; rat liver 0.3 pmol/min/mg), forming 15-keto and 13,14-dihydro-15-keto metabolites as determined by TLC, HPLC and GC/MS. Prostaglandin D2 was not transformed in similar fashion in NAD+- or NADP+-supplemented incubations in any of the 12 cytosolic systems. However, PGD2 was converted to a single product identified by TLC, HPLC and GC/MS as 9 alpha, 11 beta-PGF2 in certain of the systems when supplemented with an NADPH regenerating system, with high activity in guinea-pig kidney (55.0 pmol/min/mg), guinea-pig liver (27.5 pmol/min/mg) and rabbit liver (13.7 pmol/min/mg) and less than 5 pmol/min/mg in 8 of the remaining 9 systems. This stereospecific 11-ketoreductase of rabbit and guinea-pig liver was stable to 10 min heating at 50 degrees, dialysis, storage at -20 degrees and repeated freeze/thawing but was not inhibited by sulphasalazine analogues. The 11-ketoreductase had a markedly different tissue profile from PGE2 9-ketoreductase, which was shown to convert PGE2 stereospecifically to 9 alpha, 11 alpha-prostaglandin F2 (PGF2 alpha) and was present at highest activity in rabbit liver and kidney. Evidence was obtained that 9 alpha, 11 beta-PGF2 was actively transformed by the sulphasalazine-inhitable 15-PGDH pathway at approximately one third of the rate of PGF2 alpha with high activity in several cytosolic systems (e.g. rat caecum, guinea-pig liver and kidney), suggesting that further transformation in vivo of this biologically active product of PGD2 metabolism could be initiated by this route.

Prostaglandin-E2 9-ketoreductase from human uterine decidua vera

Prostaglandin-E2 9-ketoreductase, the enzyme which catalyzes the reaction from prostaglandin E2 (PGE2) to prostaglandin F2 alpha (PGF2 alpha), has been purified 232-fold from human uterine decidua vera. The molecular mass of the enzyme, as estimated by fast protein liquid chromatography, was 29 kDa. Sodium dodecyl sulfate disc gel electrophoresis of the denatured enzyme revealed a molecular mass of 31 kDa. These data suggest that the enzyme consists of a single polypeptide chain. The rate equation of the enzyme reaction for two substrates was used for the determination of five kinetic constants. The equilibrium constant with respect to PGE2 was 83 microM, the Michaelis constant, Km, for PGE2 was 93 microM. For NADPH, the equilibrium constant was 1.0 microM and Km was 1.6 microM. The maximal velocity for the forward reaction was V1 = 217 pmol/min. The inhibition constants for the analgesic agents indomethacin and fentiazac were Ki = 850 microM and Ki = 450 microM and for the steroid progesterone Ki = 1.5 mM, respectively. Prostaglandin-E2 9-ketoreductase might be responsible for the control of the PGE2/PGF2 alpha ratio in human decidua vera. The enzyme, therefore, might be an important factor in the cascade of events leading to uterine contractions and parturition.

Identification of pig brain aldehyde reductases with the high-Km aldehyde reductase, the low-Km aldehyde reductase and aldose reductase, carbonyl reductase, and succinic semialdehyde reductase

Four NADPH-dependent aldehyde reductases (ALRs) isolated from pig brain have been characterized with respect to substrate specificity, inhibition by drugs, and immunological criteria. The major enzyme, ALR1, is identical in these respects with the high-Km aldehyde reductase, glucuronate reductase, and tissue-specific, e.g., pig kidney aldehyde reductase. A second enzyme, ALR2, is identical with the low-Km aldehyde reductase and aldose reductase. The third enzyme, ALR3, is carbonyl reductase and has several features in common with prostaglandin-9-ketoreductase and xenobiotic ketoreductase. The fourth enzyme, unlike the other three which are monomeric, is a dimeric succinic semialdehyde reductase. All four of these enzymes are capable of reducing aldehydes derived from the biogenic amines. However, from a consideration of their substrate specificities and the relevant Km and Vmax values, it is likely that it is ALR2 which plays a primary role in biogenic aldehyde metabolism. Both ALR1 and ALR2 may be involved in the reduction of isocorticosteroids. Despite its capacity to reduce ketones, ALR3 is primarily an aldehyde reductase, but clues as to its physiological role in brain cannot be discerned from its substrate specificity. The capacity of succinic semialdehyde reductase to reduce succinic semialdehyde better than any other substrate shows that this reductase is aptly named and suggests that its primary role is the maintenance in brain of physiological levels of gamma-hydroxybutyrate.

Prostaglandin-9-ketoreductase activity in erythrocytes of normal and hypertensive subjects

The PGE2/PGF2 alpha balance, controlled in part by prostaglandin-9-ketoreductase, seems to be involved in the regulation of sodium excretion by the kidney. A decreased PGE2/PGF2 alpha ratio has been observed in the urine of hypertensive subjects. This suggests that an alteration of prostaglandin metabolism might be involved in the pathogenesis of essential hypertension. In order to test this hypothesis, prostaglandin-9-ketoreductase (PG-9-KR) and prostaglandin-15-dehydrogenase (PG-15-DH) activities were measured in erythrocytes of normotensive controls and patients with essential hypertension. The two enzyme activities were highly correlated in the two groups, supporting the hypothesis that they are alternate expressions of a single enzyme. These two enzyme activities were not significantly different in hypertensive subjects as compared to controls. Human essential hypertension does not appear to be linked to a generalized defect of prostaglandin catabolic enzymes.

Purification of prostaglandin E2-9-oxoreductase from human decidua vera

Prostaglandin E2-9- oxoreductase (PGE2-9-OR), the enzyme which converts prostaglandin E2 (PGE2) to prostaglandin F2 alpha (PGF2 alpha), has been detected in human decidua vera. A 105-fold purification was achieved when the centrifuged homogenate was fractionated sequentially by DEAE-Trisacryl, hydroxyapatite-agarose gel, ultrogel AcA 44 and Matrex gel blue A gel chromatographies. The following kinetic constants for PGE2-9-OR have been obtained. The equilibrium constant with respect to PGE2 is 83 microM, the Michaelis constant, Km, for PGE2 is 80 microM, for NADPH 1.6 microM. The maximal velocity for the forward reaction is V1 = .203 pmol/min. The enzyme was inhibited by progesterone, oestradiol-17 beta, cortisol and pharmaceutical drugs. An activating effect could be demonstrated with Ca2+ and oxytocin. The occurrence of PGE2-9-OR in the decidua vera suggests that this enzyme may be responsible for the transformation of PGE2 to PGF2 alpha in these tissues. This may be an important mechanism for the initiation and maintenance of uterine contractions.

Enzymatic inactivation of 6-keto-prostaglandin E1 in vitro: Comparison with prostaglandin E1

The inactivation of 6-keto PGE1, a biologically active and stable metabolite of prostacyclin, was studied in 100,000 g cytosolic supernatants by bioassay on rat stomach strip (contraction) and human platelets (inhibition of ADP-induced aggregation). PGE1 was used as a reference compound. Both PGs were inactivated in supernatants from colon, kidney and liver of rat, rabbit and guinea-pig. Inactivation was time- and NAD+ -dependent and was generally greater for PGE1 than 6-keto-PGE1. The enzyme responsible for 6-keto-PGE1 inactivation in cytosolic supernatants is distinct from prostaglandin 15-hydroxydehydrogenase and 9-keto reductase, is not inhibitable by sulphasalazine-like drugs and its activity is recoverable after precipitation by ammonium sulphate. We conclude that 6-keto-PGE1 can be inactivated by enzymes with wide tissue distribution, but further studies are needed for identification of these novel enzymes and the products formed as well as to assess their significance in the intact animal.

Alpha adrenergic stimulation modified prostaglandins release in vas deferens

Methoxamine enhanced contractions of mouse vasa deferentia through alpha adrenoceptor stimulation. Additionally, the generation of PGF-like material by the tissue was increased by methoxamine, whereas that of PGE-like material was decreased. The effects of methoxamine on prostaglandin output (stimulation and depression) were antagonized by yohimbine and phenoxybenzamine. Moreover, the stimulating influence of methoxamine on the contractile activity of the preparations was attenuated by the prostaglandin synthesis inhibitors indomethacin and acetylsalicylic acid. The results suggest that methoxamine is able to modify prostaglandin synthesis and output in mouse vasa deferentia, probably through an alpha adrenergic mediated mechanism coupled to the prostaglandin synthesizing system. The fact that indomethacin and acetylsalicylic acid blocked alpha stimulatory responses to methoxamine, suggest a modulatory role for endogenous prostaglandins. Since methoxamine increased PGF levels, this prostaglandin might potentiate the contractile influence of methoxamine.

A radioimmunoassay for 6-ketoprostaglandin E1

A radioimmunoassay for 6-ketoprostaglandin E1 has been developed. 6-keto-prostaglandin E1 antibodies were produced in rabbits by repeated immunization with 6-ketoprostaglandin E1 coupled to bovine serum albumin. [125]-labeled hapten with high specific radioactivity was prepared by radioiodination of 6-ketoprostaglandin in E1-tyrosine methyl ester conjugate followed by purification with thin layer chromatography. The antibodies showed good specificity toward 6-ketoprostaglandin E1 and crossreacted only significantly with prostaglandin E1. The sensitivity of the assay was 10 pg per assay tube. Application of the radioimmunoassay was demonstrated by the detection of immunoreactive 6-ketoprostaglandin E1 from 6-ketoprostaglandin F1 alpha catalyzed by swine renal NADP+-linked 9-hydroxyprostaglandin dehydrogenase.