Purification and properties of nucleotide pyrophosphatase from human placenta

Nucleotide pyrophosphatase was purified from human placenta to near homogeneity with a specific activity of about 500-fold over the Triton extract of the homogenate. Purification was achieved most effectively by successive chromatographic steps with AMP-agarose and ADP-agarose columns, based on the affinity of the enzyme towards 5'-adenylate and adenosine 3',5'-diphosphate, and a lectin-Sepharose column, based on the glycoprotein nature of the enzyme. The purified enzyme was found to be essentially homogeneous on SDS-polyacrylamide gel electrophoresis with a mobility corresponding to 130K. The purified enzyme was found to hydrolyze a wide variety of nucleotides, i.e. 3'-phosphoadenosine 5'-phosphosulfate (PAPS), adenosine 5'-phosphosulfate (APS), NADH, ATP, nucleotide sugars, oligonucleotides, and p-nitrophenyl-thymidine 5'-phosphate (PNTP). From the oligonucleotides, the enzyme produced 5'-phosphates. Mg2+ was required for full activity. Glycine and sulfhydryl compounds such as 2-mercaptoethanol and 2,3-dimercapto-1-propanol were inhibitory. Most of these properties are common to nucleotide pyrophosphatases [EC 3.6.1.9] and type I (5'-phosphate forming) phosphodiesterases [EC 3.1.4.1] from various sources. The relevance of this enzyme to a unique genetic disease, Lowe's syndrome, is discussed.     

Purification and kinetic properties of galactokinase from human placenta

Galactokinase from human placenta was purified about 350-fold using DEAE-Sephadex-A-50 chromatography followed by Sephadex-G-200 and CM-Sephadex-C-50 filtration. The final steps of purification involved electrofocusing and ammonium sulfate precipitation. In analytical disc electrophoresis the purified enzyme moved as a single protein band.     

Purification and properties of arylsulfatase C from human placenta

Arylsulfatase C (ASC) was purified about 1,000-fold from human placenta. The major steps in the procedure included chromatography on Con A-Sepharose and Bio-Gel A-1.5 m. The purified enzyme was homogeneous by sodium dodecylsulfate/polyacrylamide gel electrophoresis. The native enzyme has an apparent molecular weight of 238,000 resulting from three identical subunits of 78,000 daltons. The purified enzyme hydrolyzes the artificial substrate p-nitrophenyl sulfate (NPS), and the two natural substrates estronesulfate (ES) and dehydroepiandrosterone sulfate (DHEAS), the ratio of these three activities being constant throughout the purification. ES and DHEAS are powerful competitive inhibitors of the enzymatic hydrolysis of NPS. ASC, ESase and DHEASase activities show the same thermal stability. These results strongly suggest that a single enzyme is responsible for the hydrolysis of the two natural and the artificial substrates.     

Purification and various properties of uracil-DNA-glycosylase from human placenta

Uracil-DNA-glycosylase was isolated from human placenta and purified 2100-fold. The apparent Km value for non-methylated DNA substrate of the enzyme is 3.10(-7) M. However, Km for uracil-DNA-glycosylase was 3 times as low when methylated DNA was used as a substrate. It was shown that the initial rate of uracil excision was greater for the non-methylated than for the hypermethylated DNA. The experimental results indicate that the postreplicative methylation of DNA can interfere with uracil excision.     

Purification and properties of aldehyde reductases from human placenta

Aldehyde reductases (alcohol: NADP⁺-oxidoreductases, EC 1.1.1.2) I and II from human placenta have been purified to homogeneity. Aldehyde reductase I, molecular weight about 74 000, is a dimer of two nonidentical subunits of molecular weigths of about 32 500 and 39 000, whereas aldehyde erductase II is a monomer of about 32 500. Aldehyde reductase I can be dissociated into subunits under high ionic concentrations. The isoelectric pH for aldehyde reductases I and II are 5.76 and 5.20, respectively. Amino acid compositions of the two enzymes are significantly different. Placenta aldehyde reductase I can utilize glucose with a lower affinity, whereas aldehyde reductase II is not capable to reducing aldo-sugars. Similarly, aldehyde reductase I does not catalyse the reduction of glucuronate while aldehyde reductase II has a high affinity for glucuronate. Both enzymes, however, exhibit strong affinity towards various other aldehydes such as glyceraldehyde, propionaldehyde, and pyridine-3-aldehyde. The pH optima for aldehyde reductases I and II are 6.0 and 7.0, respectively. Aldehyde reductaase I can use both NADH and NADPH as cofactors, whereas aldehyde reductase II activity is dependent on NADPH only. Both enzymes are susceptible to inhibition by sulfhydryl group reagents, aldose reductase inhibitors, lithium sulfate, and sodium chloride to varying degrees.     

Ribonuclease inhibitor from human placenta. Purification and properties

A soluble ribonuclease inhibitor from the human placenta has been purified 4000-fold by a combination of ion exchange and affinity chromatography. The inhibitor has been isolated in 45% yield (about 2 mg/placenta) as a protein that is homogeneous by sodium dodecyl sulfate-gel electrophoresis. In common with the inhibitors of pancreatic ribonuclease from other tissues that have been studied earlier, the placental inhibitor is an acidic protein of molecular weight near 50,000; it forms a 1:1 complex with bovine pancreatic RNase A and is a noncompetitive inhibitor of the pancreatic enzyme, with a Ki of 3 X 10(-10) M. The amino acid composition of the protein has been determined. The protein contains 30 half-cystine plus cysteine residues determined as cysteic acid after performic acid oxidation. At pH 8.6 the nondenatured protein alkylated with iodoacetic acid in the presence of free thiol has 8 free sulfhydryl groups. The inhibitor is irreversibly inactivated by sulfhydryl reagents and also by removal of free thiol from solutions of the protein. Inactivation by sulfhydryl reagents causes the dissociation of the RNase - inhibitor complex into active RNase and inactive inhibitor.     

DNA ligases from rat liver. Purification and partial characterization of two molecular forms

The differential ability of mammalian DNA ligases to use oligo(dT).poly(rA) as a substrate has been used to detect, and thereby extensively purify, two immunologically distinct forms of DNA ligase from rat liver. The activity of DNA ligase I, which is unable to use this template, is uniquely increased during liver regeneration, while that of DNA ligase II remains at a low level. Both enzymes require ATP and Mg2+ for activity and form an adenylylated intermediate which is stable and reactive. After SDS-PAGE, such radiolabeled complexes correspond to polypeptides of 130,000 and 80,000 Da for DNA ligase I and to 100,000 Da for DNA ligase II. That these labeled polypeptides do indeed correspond to active polypeptides of two different forms of DNA ligase is shown by the removal of the radiolabeled AMP, only when the intermediate is incubated with an appropriate substrate. In contrast to other eukaryotic DNA ligases, rat liver DNA ligase II has a lower Km for ATP (1.2 X 10(-5) M) than DNA ligase I (6 X 10(-5) M). Also, DNA ligase II can use ATP alpha S as a cofactor in the ligation reaction much more efficiently than DNA ligase I, further discriminating the ATP binding sites of these enzymes. Finally, antibodies raised against the 130,000-Da polypeptide of DNA ligase I specifically recognize this species in an immunoblot and inhibit only the activity of DNA ligase I.     

Purification and properties of L-lysine-alpha-ketoglutarate reductase from human placenta.

l-Lysine-α-ketoglutarate reductase has been extensively purified from human placenta. The enzyme is active in the formation of saccharopine from l-lysine and α-ketoglutarate and possesses a stringent substrate specificity. Steady-state product inhibition studies indicate the possibility of either of two basic reaction mechanisms. The first is an ordered reaction mechanism in which α-ketoglutarate, l-lysine, and NADPH bind to the enzyme followed by the release of NADP and saccharopine. The second mechanism involves an initial binding of NADPH. This is followed by either the ordered addition of α-ketoglutarate and l-lysine with the occurrence of an E-NADPH-saccharopine dead-end complex or by the random addition of α-ketoglutarate and l-lysine with the formation of an E-NADPH-sac-charopine-l-lysine dead-end complex. No inhibition of the forward reaction or stimulation of the reverse reaction by the addition of ammonium sulfate was found; other investigators, working with other mammalian tissue have reported such effects. A molecular weight estimate of 480,000 for both l-lysine-α-ketoglutarate reductase and saccharopine dehydrogenase was obtained on gel filtration. No indication of separation of the two activites was obtained throughout the purification procedure, and the presence of detergents had no effect on the sedimentation rate in the ultracentrifuge or on the migration rate in gel filtration.     

Purification and properties of glutathione peroxidase from human placenta.

Glutathione peroxidase (glutathione--H2O2 oxidoreductase; EC 1.11.1.9) was purified to homogeneity from human placenta by using (NH4)2SO4 precipitation, ion-exchange chromatography, Sephadex gel filtration and preparative polyacrylamide-disc-gel electrophoresis. Glutathione peroxidase from human placenta is a tetramer, having 4g-atoms of selenium/mol of protein. The molecular weight of the enzyme is about 85000 with a subunit size of about 22,000. Kinetic properties of the enzyme are described. On incubation with cyanide, glutathione peroxidase is completely and irreversibly inactivated and selenium is released as a low-molecular-weight fragment. Reduced glutathione, beta-mercaptoethanol and dithiothreitol protect the enzyme from inactivation by cyanide and the release of selenium. Properties of human placental glutathione peroxidase are similar to those of isoenzyme A reported earlier by us from human erythrocytes. The presence of isoenzyme, B, reported earlier by us in human erythrocytes, was not detected in placenta. Also selenium-independent glutathione peroxidase (isoenzyme II), which is specific for cumene hydroperoxide, was not present in human placenta.     

Purification and properties of steroid sulfatase from human placenta.

Steroid sulfatase was purified approximately 170-fold from normal human placental microsomes and properties of the enzyme were investigated. The major steps in the purification procedure included solubilization with Triton X-100, column chromatofocusing, and hydrophobic interaction chromatography on phenylsepharose CL-4B. The purified sulfatase showed a molecular weight of 500-600 kDa on HPLC gel filtration, whereas the enzyme migrated as a molecular mass of 73 kDa on sodium dodecyl sulfate polyacrylamide gel electrophoresis. The isoelectric point of steroid sulfatase was estimated to be 6.7 by isoelectric focusing in polyacrylamide gel in the presence of 2% Triton X-100. The addition of phosphatidylcholine did not enhance the enzyme activity in the placental microsomes obtained from two patients with placental sulfatase deficiency (PSD) after solubilization and chromatofocusing. This result indicates that PSD is the result of a defect in the enzyme rather than a defect in the membrane-enzyme structure. Amino acid analysis revealed that the purified human placental sulfatase did not contain cysteine residue. The Km and Vmax values of the steroid sulfatase for dehydroepiandrosterone sulfate (DHA-S) were 7.8 microM and 0.56 nmol/min, while those for estrone sulfate (E1-S) were 50.6 microM and 0.33 nmol/min, respectively. The results of the kinetic study suggest the substrate specificity of the purified enzyme, but further studies should be done with different substrates and inhibitors.     

Purification and properties of factor XIII from human placenta.

1. FXIII was isolated and purified over 4000 fold from human placenta to apparent electrophoretic homogeneity by a new procedure including ethanol precipitation. DEAE-Cellulose, molecular sieving on Sephacryl S-300 and Phenyl-Sepharose chromatography. 2. Its pI was about 5.1. Under appropriate conditions, the incubation of FXIII in the presence of thrombin did not lead to inactivation cut in the polypeptidic chain. 3. FXIII was also activated by CaCl2 and, in a lesser extent, by other divalent cations like SrCl2, BaCl2 or MgCl2. 4. The binding of calcium to FXIII exhibited a negative cooperativity. 5. The activity-pH curve of the calcium-activated enzyme did not appear very different from that of the thrombin-activated enzyme.     

N-Acetylaminoacyl-p-nitranilidase from human placenta. Purification and some properties.

An enzyme hydrolyzing N-acetylaminoacyl-p-nitroanilides has been isolated from mature human placentae by a six-step procedure comprising extraction from a placenta homogenate, ammonium sulfate fractionation, treatment with isopentyl alcohol, chromatography on CM-Sephadex, protamine sulfate precipitation and gel filtration on an Ultrogel AcA 34 column. About 2500-fold enrichement was achieved from placenta homogenate. The purified enzyme preparation showed a single band on polyacrylamide disc electrophoresis. The molecular weight was estimated to be 380,000 by gel filtration. Placental extracts contain two main isoenzymes of pI 3.9 and 4.5 respectively. Activity was strongly inhibited by chloromercuribenzoate, slightly inhibited by Ca2+ and cysteine; no activation could be detected. The enzyme exhibits an exopeptidase-like activity towards acetyl-dipeptides with a certain specifity towards N-acetylalanyl-alanine; N-acetylalanine-p-nitroanilide, however, is hydrolyzed four times faster. With N-acetylalanine-p-nitroanilide as substrate the pH optimum was 8.0--8.2; Km was 2.13 mmol/l. N-Acetylleucine-p-nitroanilide and N-acetyltyrosine-p-nitroanilide were split slowly; N-acetylalanyl-alanyl-alanine-p-nitroanilide, N-butyloxycarbonyl-alanyl-alanine-p-nitroanilide, unsubstituted analogous aminoacyl-p-nitroanilides and several protein substrates were not hydrolyzed. The functions of the enzyme are still unknown.     

Purification and properties of N-acetylgalactosamine 6-sulphate sulphatase from human placenta

1. N-Acetylgalactosamine 6-sulphate sulphatase was purified about 20000-fold from the soluble extract of human placenta with N-acetylgalactosamine 6-sulphate-glucuronic acid-N-acetyl[1-(3)H]galactosaminitol 6-sulphate as substrate in the activity assay. The enzyme appears to be a glycoprotein with a mol.wt. of about 100000 as determined by gel filtration. On gel electrophoresis in the presence of sodium dodecyl sulphate the major protein band had a mol.wt. of 78000. Variable charge heterogeneity was observed in several enzyme preparations. 2. The purified enzyme released up to one sulphate molecule from the disulphated trisaccharide. It was active towards N-acetylgalactosamine 6-sulphate and exhibited no measurable N-acetylglucosamine 6-sulphate sulphatase or any other known lysosomal sulphatase activity. Hydrolysis of [1-(3)H]galactitol 6-sulphate was achieved by incubation neither with a crude nor with a purified enzyme preparation. Chondroitin 6-sulphate and keratan sulphate, as well as heparin and heparan sulphate, served as competitive inhibitors of the enzyme. 3. Purified N-acetylgalactosamine 6-sulphate sulphatase activity was optimal at pH4.9 and 4.4 when assayed in 0.02m-sodium acetate buffer and at pH4.2 and 5.2 in 0.1m-sodium acetate buffer. A single pH-optimum at pH4.8 was observed for the crude enzyme and for the purified enzyme after mild periodate treatment. The sulphatase activity was inhibited by a variety of anions and cations and activated by thiol-specific and thiol reagents.     

Purification and properties of mitochondrial monoamine oxidase type A from human placenta

A high yield purification scheme for monoamine oxidase A from human placental mitochondria is described. The enzyme is solubilized by a combination of treatment with phospholipase A and C and extraction with Triton X-100 and further purified by partitioning between dextran and polyethylene glycol polymers. The enzyme was obtained in 35% yield and high purity on DEAE-Sepharose CL-6B chromatography. This product, 90% catalytically active, showed a single major and several minor bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Further purification could be achieved by additional chromatography using Bio-Gel HTP, but concomitant loss of catalytic activity occurred (enzyme remained about 60% active). The difference extinction coefficient for flavinox--flavinred at 456 nm was 10,800 +/- 350 m-1 cm-1. A sulfhydryl to flavin ratio of 7.5 was obtained when enzyme was denatured with sodium dodecyl sulfate, reduced with 2-mercaptoethanol, and titrated with 2,2'-dipyridyl disulfide. Anaerobic titration with 0.5 eq of sodium dithionite gave rise to the red anionic flavin radical, and full reduction was observed on further addition of reagent. The Km value for kynuramine was essentially the same for mitochondria (0.12 mM) and enzyme after DEAE-Sepharose CL-6B chromatography (0.17 mM). The concentration of clorgyline and deprenyl required for 50% inactivation also remained essentially unchanged. Incubation of the enzyme with 2,2'-dipyridyl disulfide caused inactivation in a biphasic manner with apparent second-order rate constants of 1230 M-1 min-1 and 235 M-1 min-1 for the rapid and slow phase, respectively. This inactivation was largely abolished by the inclusion of the competitive inhibitor amphetamine (Ki = 20 microM) in the incubation mixture. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated a subunit molecular mass of 60-64 kDa, about 1.5-2.5 kDa higher than human liver monoamine oxidase B.     

Purification and properties of human placenta arylsulphatase A.

1. Arylsulphatase A (arylsulphate sulphohydrolase E.N. 3.1.6.1) has been purified 7200-fold from human placenta using concanavalin A Sepharose chromatography. 2. Ultracentrifugation studies indicated that the purified enzyme was homogenous with respect to sedimentation coefficient and molecular weight and has a molecular weight of 102000. 3. The purified enzyme could hydrolyze cerebroside 3-sulphate, seminolipid and sulphogalactosylsphingosine under identical conditions. 4. The kinetic parameters for the hydrolysis of all sulphate esters used in the present study were the same. 5. Both seminolipid and sulphogalactosylsphingosine were competitive inhibitors for the hydrolysis of cerebroside-3-sulphate with an inhibition constant of 0.2 mM. 6. Kinetic parameters, metal ion effect and heat inactivation profile of enzyme suggest that the same active site of enzyme is responsible for the hydrolysis of cerebroside 3-sulphate, seminolipid and sulphogalactosylsphingosine.