[5] γ-Glutamyl transpeptidase, a leukotriene metabolizing enzyme

38

ENZYMES AND RECEPTORS:

PURIFICATION

A N D ASSAY

[5]

[5] 7 - G l u t a m y l T r a n s p e p t i d a s e , a L e u k o t r i e n e Metabolizing Enzyme

By

KERSTIN

BERNSTROM,

LARS ORNING,

and SVEN HAMMARSTROM

Leukotriene C + acceptor ~.~ leukotriene D + ~/-glutamyi-acceptor (acceptor: water, a m i n o acid, or dipeptide)

Leukotrienes are a new group of biological mediators that probably have important roles in inflammatory and allergic responses? They are formed from several polyunsaturated fatty acids that are converted to epoxides having three conjugated double bonds (leukotrienes A). Hydroperoxy derivatives, formed by lipoxygenase(s), are intermediates in these reactions. The epoxides are further transformed in two ways: by enzymic hydrolysis into dihydroxy acids (leukotrienes B) or by enzymic addition of glutathione to give leukotrienes C (LTC). The latter products, in addition to glutathione and glutathione disulfide, are endogenous substrates for 3~-glutamyl transpeptidase (y-glutamyltransferase, EC 2.3.2.2). Preparation of Leukotrienes C The enzyme can utilize the following LTC-type leukotrienes as substrates: Ca, C4, C5, 8,9-Ca as well as ll-trans isomers of C3, C4, and C5. No appreciable differences in the rate of conversion of the different C-type leukotrienes has been observed. The substrates can be prepared biosynthetically from the appropriate precursor fatty acid by incubating the acid with murine mastocytoma cells stimulated with Ca2+ ionophore (A 23187).

Reagents Incubation buffer: 150 mM NaC1, 3.7 mM KC1, 3.0 mM Na~HPO4, 3.5 mM KH~PO4, 0.9 mM CaC12, 5.6 mM dextrose, pH 7 CXBGABMCT-1 murine mastocytoma cells, 107 per milliliter L-cysteine, 0.2 M, dissolved in incubation buffer A 23187, 4 mM, and 10-20 mM precursor fatty acid, in 99% ethanol The precursor fatty acids are eicosatrienoic acid (n-9), arachidonic acid, eicosapentaenoic acid (n-3), and eicosatrienoic acid (n-6) (dihomoi B. S a m u e l s s o n and S. H a m m a r s t r 6 m , Vitam. Horm. (N. Y.),in p r e s s (1982).

METHODS IN ENZYMOLOGY, VOL, 86

Copyright © 1982by Academic Press, Inc. All rights of reproduction in any form reserved. ISEN 0-12-181986-8

[5]

T-GLUTAMYLTRANSPEPTIDASE AND LEUKOTRIENES

39

y-linolenic acid) for leukotrienes Ca, C4, C5, and 8,9-C3, respectively. 2-5 Mastocytoma Cells. Murine mastocytoma cells (CXBGABMCT-1) 3 are kept as intramuscular tumors in hind legs of CXBG or CB6F-1 mice. When the tumors reach a size of 0.5-1.5 cm 3 (17-20 days after injection), the animal is killed by excessive ether anesthesia. The tumors from both legs are rapidly excised and minced (e.g., using the blunt side of a Pasteur pipette) in 5 - 7 ml of sterile phosphate-buffered saline. Large tissue fragments are allowed to sediment for 5 min. The tumor cell suspension is then injected intraperitoneally (0.2 ml) or intramuscularly (0.1 ml per leg) into the same kinds of mice. A disposable 1-ml plastic syringe and a 25gauge ~-inch needle are used for the injections. Two weeks later, intraperitoneally injected animals are killed by decapitation under ether anesthesia. The abdominal skin is removed, and 5 ml of incubation buffer are injected through the peritoneum. After gentle massage of the abdomen, the fluid containing the ascites tumor cells is collected in a plastic beaker on ice after incision of the peritoneum with a pair of scissors. The peritoneal cavity is then rinsed several times with 1-ml portions of incubation buffer. Care is taken to avoid contamination by blood, bile, or urine. The mastocytoma cells are sedimented by a centrifugation in plastic tubes (250 g, 15 min, 4°). If contaminated by more than 1-2% erythrocytes, the sediments are resuspended in 5 ml of 0.155 M NI-I4C1-0.17 M Tris-HCl, pH 7.4 (9: 1, v/v, freshly mixed) and incubated at 37° for 5 rain. After centrifugation, the sediments are finally resuspended in 5 ml of incubation buffer (a 1-ml automatic pipette with a plastic tip is used for the resuspension). Cell concentration is determined with a hemacytometer and using a 100-fold dilution of the cell suspension. Up to this point the cells are kept at 0 - 4 ° . Incubations) Additional incubation buffer (37°) is added to make the cell concentration 107/ml. The cells are incubated in a plastic jar at 37° for 15-30 min. L-Cysteine solution is added (5% v/v), and incubation is continued for 2 min to allow synthesis of glutathione. The solution of ionophore and precursor fatty acid (0.5% v/v), is added dropwise and incubation is continued for another 20 min, with shaking. Four volumes of ethanol are added, and the whiteprecipitate that forms after 3-16 hr at 4° is removed by filtration. The solvents are removed by rotary evaporation (water bath at 30°). When nearly dry, water (10-20% of the incubated volume) is added and the sample is applied to a column of Amberlite XAD-8 2 S. HammarstrOm, 3 R. C. Murphy, S. 4275 (1979). 4 S. HammarstrOm, 5 S. Hammarstr6m,

J. Biol. Chem. 256, 2275 (1981). HammarstrOm, and B. Samuelsson, Proc. Natl. Acad. Sci. U.S.A. 76, J. Biol. Chem. 255, 7093 (1980). J. Biol. Chem. 256, 7712 (1981).

40

ENZYMESAND RECEPTORS: PURIFICATION AND ASSAY

[5]

TABLE I ELUTION BEHAVIOR OF LEUKOTRIENES ON REVERSED-PHAsE HIGH-PERFORMANCE LIQUID CHROMATOGRAPHYa

Elution times (min) Isomers

LTCa

LTDs

LTC4

LTD4

LTC5

LTD5

11-cis 11-trans

15.6 17.4

25.2 27.2

10.0 12.2

15.6 17.6

7.0 9.0

I 1.0 13.2

8,9-LTCa

8,9-LTD3

Prostaglandin B2

9.4

14.5

10.0

Column, C~ Nucleosil (250 x 4.6 mm); solvent, methanol-water, 7:3 (v/v)-0.1% acetic acid, adjusted to pH 5.4 with NI-LOH;flow, 1 ml/min.

having the same volume. After application and elution with one more volume of water, two volumes, of 80% aqueous ethanol are used to elute leukotrienes. This eluate is concentrated to dryness on a rotary evaporator, and the residue is dissolved in methanol (10 ml). Silicic acid (SilicAr CC7, 0.5 g) is added, and the methanol is evaporated to coat the residue on the silicic acid powder. This is transferred to the top of a 3.5-g column of SilicAr CC-7, packed in diethyl ether-hexane, 3:7 (v/v). The column is then eluted with 50-ml portions of the same solvent, ethyl acetate, 5, 10, and 50% (v/v) methanol in ethyl acetate. Leukotrienes are eluted with 50 ml of methanol. After evaporation of the methanol, the residue is dissolved in 2 ml of methanol-water, 7 : 3 (v/v), also containing 0.1% acetic acid and adjusted to pH 5.4 with NI-I4OH. Nondissolved material is removed by centrifugation (500 g, 5 min), and the solution is injected to a Cls Polygosil (500 x 10 mm) reversed-phase high-performance liquid chromatography (HPLC) columns eluted with the same solvent (4.5 ml/min). Leukotrienes are detected from their absorption of ultraviolet light at 280 nm. Approximate elution volumes for leukotrienes, during subsequent analyses on a smaller column, are given in Table I. Characterization of Leukotrienes C and D Leukotrienes (24 and Cs have characteristic ultraviolet (UV) spectra with absorbance maximum at 280 nm and shoulders at 270 and 291 nm. 3'4 The spectrum is due to the presence of a conjugated triene chromophorc with an allylic thioether substituent. The spectra of leukotriene C3 and 8,9leukotriene Ca have absorbance maxima at 279 nm and shoulders at 269 and 290 nm. 2.5 The products obtained by treating these leukotrienes with

[5]

T-GLUTAMYLTRANSPEPTIDASE AND LEUKOTRIENES

41

7-glutamyl transpeptidase (leukotrienes D4, Ds, D3, and 8,9-Da) have the same UV spectra as the corresponding precursor leukotriene C. 11-trans Isomers of leukotrienes have UV spectra that are shifted 2 nm hypsochromatically in comparison to the 11-cis compounds (hmax at 278 and 277 nm, respectively2,6). The conjugated triene in leukotrienes C4, Cs, D4, and D5 is extended to a conjugated tetraene by treatment of the compounds with soybean lipoxygenase,a This enzyme acts on polyunsaturated fatty acids containing two methylene-interrupted cis double bonds at the to-6 and to-9 positions. One molecule of 02 is introduced at to-6, and the to-6 double bond is isomerized to to-7. The conversions of leukotrienes (2.5 nmol, dissolved in 1 ml of Tyrode's buffer) with soybean lipoxygenase (10/xg) is monitored by ultraviolet spectroscopy. A 28-nm bathochromic shift of the spectrum is observed if the leukotriene contains cis double bonds at the All and A14 positions and additional double bonds at A7 and Aa. Further characterization can be achieved by amino acid analyses after hydrolyses and by gas-liquid chromatography-mass spectrometry after catalytic desulfurization. For amino acid analysis, approximately 2 nmol of leukotriene (based on the absorbance at 280 nm; ~ = 40,000) is introduced into a glass ampoule; the solvent is evaporated under a stream of nitrogen, and 0.5 ml of 6 N HC1-0.5% phenol, containing 10 nmol of norleucine as internal reference, is added. The ampoule is evacuated, using an oil pump, to a pressure of less than 0.05 mm of Hg and sealed. After 21 hr at 110°, the ampoule is allowed to cool to room temperature, then opened; the residual HCI is removed by evaporation under vacuum over KOH. The residue is dissolved in application buffer for the amino acid analyzer (Beckman 121 M or other instrument with similar sensitivity). For mass spectrometric analyses, 5 - l 0 nmol of leukotriene in 0.5 ml of ethanol are mixed with Raney nickel (W-2) suspension (10 mg in 0.5 ml of ethanol). The mixture is stirred for 30 min at 70°, cooled to room temperature, diluted with 1 ml of 1 N HC1, and extracted twice with diethyl ether. The washed extracts are evaporated to dryness, and the residue is treated in succession with ethereal diazomethane and pyridine-hexamethyldisilazane-trimethylchlorosilane, 5 : 2 : 1, v / v / v (50/xl) to convert the product into methyl ester, O-trimethylsilyl derivative. The derivative has a C value of 21.5 when analyzed on a column of 3% OV-17. The mass spectrum 3 has intense ions at role 399, 367,313, and 203, formed by elimination of "CH3, "CH3 plus CH3OH and by cleavages between C-4 and C-5 or between C-5 and C-6 with charge retention on the oxygen atom at C-5, respectively. This applies to C20 leukotrienes with a hydroxyl group at C-5 6 D. A. Clark, G. Goto, A. Marfat, E. J. Corey, S. HammarstrOm, and B. Samuelsson, Biochem. Biophys. Res. Commun. 94, 1133 (1980).

42

ENZYMES AND RECEPTORS: PURIFICATION AND ASSAY

[5]

(leukotrienes C3, C4, C5, D3, I)4, D5 and corresponding 11-trans isomers). 8,9-Substituted leukotrienes (8,9-1eukotrienes C3 and 1)3) give a derivative that has a C value of 22.0 and ions at m/e 399, 367,271, and 245 (the latter two ions formed by cleavage between C-7 and C-8 or between C-8 and C-9, respectively). 5 The amino acid analyses of C-type leukotrienes should indicate the presence of 1m o l / m o l each of glutamic acid and glycine and ca. 0.4 mol/mol of half-cystine,7 and for leukotriene D 1 mol/mol of glycine, ca. 0.4 mol/mol of half-cystine, but no glutamic acid. s Assay Method The assay is based on chromatographic (reversed-phase H P L C ) separation of substrate and product with detection of U V lightabsorption at 280 nm.

Reagents Tris-HC1 buffer, 0.1 M, pH 8 Leukotriene C, 5 - 2 0 / ~ / , in methanol-water 7: 3 (v/v)-0.1% acetic acid adjusted to pH 5.4 Enzyme, dissolved in Tris buffer Acetic acid, 0.5% (v/v) in methanol Procedure. Leukotriene C solution (0.1-0.25 ml; 0.5-5 nmol) is evaporated under a stream of argon in a small plastic tube. The dry residue is dissolved in 100/xl of Tris buffer (vortex or sonicate), and the tube is placed in a water bath at 37°. The reaction is started by addition of 10/zl of enzyme solution containing 0.1-5 mg of protein per milliliter. The reaction mixture is incubated for 30 min with gentle shaking. Acetic acid in methanol, 0.11 ml, is added to stop the reaction and precipitate the enzyme. After mixing and sedimenting the precipitate (700 g, 5 min) the clear solution is injected into a reversed-phase HPLC column (Cas Nucleosil, 250 × 4.6 mm). Methanol-water, 7: 3 (v/v)-0.1% acetic acid, adjusted to pH 5.4 with NI-I4OH, is used as mobile phase (flow rate: 1 ml/min). A UV light absorption detector, set at 280 nm, is attached to the column effluent and operated at a sensitivity of 0.01 absorbance unit for full-scale deflection of a 10 mV potentiometric recorder. The elution volumes for different leukotrienes C and D are shown in Table I. The conversions of leukotrienes C to D are ca. 90% under these conditions. In the presence of glutathione, T-glutamyl transpeptidase catalyzes the 7 S. Hammarstr6m, R. C. Murphy, B. Samuelsson, D. A. Clark, C. Mioskowski, and E. J. Corey, Biochem. Biophys. Res. Commun. 91, 1266 (1979). a L. Orning, S. Hammarstr6m, and B. Samuelss0n, Proc. Natl. Acad. Sci. U.S.A. 77, 2014 (1980).

[5]

'y-GLUTAMYLTRANSPEPTIDASE AND LEUKOTRIENES

43

reaction: leukotriene D + glutathione --> leukotriene C + cysteinylglycine. 9 The assay is performed as described above using leukotriene D (0.5 nmol) and glutathione (0.8/~mol) as substrates. The conversion of leukotriene D to C is approximately 70% under these conditions. Inhibitors. A number of inhibitors of ~-glutamyl transpeptidase have been described. These compounds also inhibit the conversion of leukotrienes C to leukotrienes D. L-Serine-borate complex is a transition-state inhibitor that acts at relatively high concentrations. At equimolar concentrations of L-serine and sodium borate, 50% inhibition of leukotriene D formation (IDs0) was observed at 11 mM concentration of each constituent. 1° Acivicin [(L-(aS,SS)-~-amino-3-chloro-4,5-dihydro-5-isoxazolacetic acid] is an irreversible inhibitor of the enzyme that reacts with the glutamyl binding site. 1~ Preincubation of the enzyme for 30 min with acivicin (0.25 mM) inhibits the conversion of leukotriene C to leukotriene D by more than 90%.

Purification Procedure Partially purified swine kidney enzyme is commercially available (Sigma Chemical Co.). These preparations are often contaminated with a dipeptidase, which will degrade lcukotnenes D further. By using a suitable enzyme to substrate ratio and a suitable incubation time, the latter reaction can be minimized. Although different batches of the commerical enzyme vary, typical conditions are 5 nmol of LTC per 100/~g of enzyme incubated 'at 37° for 30 rain. A simple purification procedure has been devised by Kozak and Tate. 11 Rat kidney brush border membranes are isolated according to the method of Malathi et al. 12 Papain-solubilized membrane proteins are fractionated by (NI-I4)2SO4 precipitation and by chromatography on Sephadex G-150. Renal cortices from male Sprague-Dawley rats are homogenized in 15 volumes ofS0 mM D-mannitol-2 mM Tris-HCl, pH 7.0, using a Potter-Elvehjem-type homogenizer. After addition of 1% (v/v) 1 M CaC12 solution, the mixture is left at 0° for 10 min (stir occasionally) and centrifuged at 3000 g for 15 min. The supernatant obtained is centrifuged for 20 min at 43,000 g. The second sediment is washed once in the same buffer

9 S. HammarstrOm, J. Biol. Chem. 256, 9573 (1981). 10 L. Orning and S. Hammarstr0m, J. Biol. Chem. 255, 8023 (1980). 11 E. M. Kozak and S. S. Tate, FEBS Lett. 122 175 (1980). 12 p. Malathi, H. Preiser, P. Fairclough, P. Mallett, and R. K. Crane, Biochim. Biophys. Acta 554, 259 (1979).

44

ENZYMES AND RECEPTORS: PURIFICATION AND ASSAY

[5]

A (125

-4 -T.

(12-

e-

O.ISN

"~ 0.1-

~ o.05tlJ

30

40 50 Fraction

6-0 70 number

8

FIG. 1. Sephadex G-150 chromatography of papain-solubilized T-glutamyl transpeptidase from rat kidney brush border membranes. Column, 1.5 x 90 cm; fractions, 1.3 ml. Modified from Kozak and TateJ 1

and then resuspended in 10 mM phosphate buffer, pH 7.4-0.15 M NaCI10 mM 2-mercaptoethanol (1 ml per gram of kidney). Papain (Sigma, 18 units/mg) is dissolved in the same buffer (10 mg/ml) and preincubated at 25 ° for 30 min. This solution (1 mg of papain per 10 mg of total membrane protein) is added to the resuspended brush border membranes, and the mixture is stirred slowly (25 °, 2 hr). After a centrifugation at 43,000 g for 30 min, (NI-h)2SO4 is added to the supernatant (90% saturation). The precipitate, collected by centrifugation (18,000 g, 30 min), is dissolved in 50 mM Tris-HC1 buffer, pH 8.0 (0.1 ml per gram of kidney) and applied to

TABLE II PURIFICATION OF T - G L U T A M Y L TRANSPEPTIDASE FROM RAT K I D N E Y a

Transpeptidase activity c

Fraction Homogenate (30 g of kidney) Brush border membranes Papain treatment followed by Sephadex G-150 chromatography

Volume (ml)

Proteinb (mg)

Total (U)

Specific (U/rag)

Yield (%)

441 29.5 2.7

3704 264 6.5

9920 6140 5150

2.7 23.3 792

(100) 62 52

a From Kozak and Tate. 1' By the method of O. H. Lowry, N. J. Rosebrough, A. L. Farr, and R. J. Randall, J. Biol. Chem. 193, 265 (1951). c Determined with 1 mM L-T-glutamyl-p-nitroanilide and 20 mM glycylglycine.

[6]

ARACHIDONIC ACID-15-LIPOXYGENASE

45

a column of Sephadex G-150 (2.5 x 100 cm), eluted with the same buffer. Fractions containing 7-glutamyl transpeptidase (Fig. 1) are combined and dialyzed against 100 volumes of water for 18 hr. After lyophilization the residue is dissolved in a small volume of water and stored frozen at - 20°. The purification is summarized in Table II. Alternative purification methods and additional properties of ~/-glutamyl transpeptidase have been recently described in this series, la 13 A. Meister, S. S. Tate, and O. W. Griffith, this series, Vol. 77, p. 237.

[6] A r a c h i d o n i c Peritoneal

Acid-15-Lipoxygenase from Rabbit Polymorphonuclear Leukocytes

By SHUH NARUMIYA and JOHN A. SALMON Arachidonic ~ 15-hydroperoxy-5,8,11,13acid + 02 eicosatetraenoic (15-HPETE) acid 15-hydroxy-5,8,11,13-eicosatetraenoic acid (15-HETE) nonenzymic 15-keto-5,8,11,13-eicosatetraenoic acid (15-ketoETE) 13-hydroxy- 14,15-epoxy-5,8,11-eicosatdenoic acid 1 l, 14,15-trihydroxy-5,8,12-eicosatrienoic acid

The enzyme reaction occurs in polymorphonuclear leukocytes as well as other tissues of various species. 1-a This reaction is distinctly different from that of fatty acid cyclooxygenase (PGH synthase), which also catalyzes peroxide formation at carbon 15 of arachidonic acid, since the lipoxygenase reaction is not inhibited by indomethacin. 4 This enzyme reaction is presumed to be the first step in the biotransformation of arachidonic acid to the 15-series of leukotrienes. 5 It is also suggested that the enzyme reaction is involved in inactivation of slow-reacting substance of anaphylaxis.6

1 p. Borgeat, M. Hamberg, and B. Samuelsson, J. Biol. Chem. 251, 7816 (1976). 2 M. Hamberg and B. Samuelsson, Biochem. Biophys. Res. Commun. 61, 942 (1974). 3 p. Borgeat and B. Samuelsson, Proc. Natl. Acad. Sci. U.S.A. 76, 2148 (1979). 4 0 . Radmark, C. Malmsten, and B. Samuelsson, FEBS Lett. 110, 213 (1980). 5 U. Lundberg, O. Radmark, C. Malmsten, and B. Samuelsson, FEBS Lett. 126, 127 (1981). 6 p. Sirois, Prostaglandins 17, 395 (1979).

METHODS IN ENZYMOLOGY, VOL. 86

Copyright ~ 1982 by Academic Press, Inc. All rights of reproduction in any form reserved. ISBN 0-12-181986-8