Purification and Properties of Alcohol Oxidase from Poria Contigua

Eur. J. Biochem. 101, 563-570 (1979) Purification and Properties of Alcohol Oxidase from Poria contigua Stephanie BRINGER, Benno SPREY, and Hermann SAHM Institut fur Biotechnologie der Kernforschungsanlage Julich GmbH (Received April 11, 1979) 1. Alcohol oxidase (alcohol : oxygen oxidoreductase) was purified 22-fold from the brown rot fungus Poriu contiguu. The final enzyme preparation was homogeneous as judged by polyacrylamide gel electrophoresis, and by sedimentation in an ultracentrifuge. The molecular weight was calculated to be 61 0 000 f 5000 from sedimentation equilibrium experiments. Electrophoresis in sodium dodecylsulfate gels and electron microscopic analysis indicate that the enzyme is an octamer composed of eight probably identical subunits, each having a molecular weight of 79000. The enzyme contains eight mol FAD/mol as the prosthetic group. 2. This alcohol oxidase oxidizes not only methanol but also lower primary alcohols (C, - C,), 2-propin-1-01 and formaldehyde. The apparent K, value for methanol is 0.2 mM, and that for formaldehyde 6.1 mM. Sodium azide was found to be a competitive inhibitor with respect to methanol. 3. The enzyme from the fungus Poriu contigua is immunologically different from the alcohol oxidase isolated from the methanol-utilizing yeast Cundidu boidinii. Furthermore antiserum raised against this enzyme did not cross-react with the alcohol oxidase from the white rot fungus Polyporus ohtusus. Evidence has been obtained that besides the well more the occurrence of alcohol oxidase in several known lignin-degrading white rot fungi, brown rot basidiomycetes was described previously [6,7]. The fungi are also able to decompose this polymer. Previ- present paper is concerned with the purification and ous studies have shown that the brown fungi attack properties of alcohol oxidase obtained from the brown the methoxyl groups more actively than the other rot fungus Poriu contiguu, which is very active both in carbons of the lignin skeleton, and oxidize them to the demethylation of lignin and in the oxidation of carbon dioxide [I, 21. This demethylation is probably the methoxyl groups to carbon dioxide. The molec- catalyzed by phenol oxidases or monooxygenases. ular, catalytic and immunochemical properties of this Using phenol oxidase purified from Polyporus versi- enzyme are compared with alcohol oxidases from color, Ishihara and Ishihara could measure the liber- methanol-utilizing yeasts and the white rot fungus ation of small amounts of methanol as a result of Polyporus obtusus. demethylase was isolated which required oxygen and from the fungus Xerocomus badius, a 4-veratrate demethylase was isolated which required oxygen and MATERIALS AND METHODS NADH, and cleaved off the methoxyl groups as form- Muter ids aldehyde [4]. So far nothing is known about the enzymes oxidiz- Freund's adjuvant was obtained from Calbio- ing the CI compounds methanol and/or formaldehyde chem (GieDen, F.R.G.). Bathophenanthroline was to carbon dioxide in brown rot fungi. Recently it has bought from Serva (Heidelberg, F.R.G.). 2,2'-Azino- been shown that in methanol-utilizing yeasts, the bis(3-ethyl-benzthiazoline 6-sulfonate), peroxidase methanol is successively oxidized to carbon dioxide from horse-radish, and calibration proteins were pur- by the enzymes alcohol oxidase, formaldehyde de- chased from Boehringer (Mannheim, F.R.G.). Ultra- hydrogenase and formate dehydrogenase [5]. Further- filter UM 10 were obtained from Amicon (Witten, F.R.G.). Formaldehyde was prepared by heating Enzyme. Alcohol oxidase or alcohol : oxygen oxidoreductase 0.5 g paraformaldehyde in 5 ml water at 100°C in a (EC 1.1.3.13). sealed tube for 15 h. Antibodies against alcohol oxi- 564 Alcohol Oxidase from Poria contigua dase from Candida boidinii were a generous gift from preparative gel electrophoresis 5-mm-thick slab gels Dr L. Eggeling of this institute. were used as described by Sprey et al. (this institute, unpublished work). The molecular weight of the poly- peptide chains was estimated according to Weber and Organisms and Growth Conditions Osborn [13]. The purified enzyme was incubated in The brown rot fungi Poria contigua and Lenzites 10 mM sodium phosphate buffer, pH 7.0, containing trabea were kindly supplied by Dr K. Haider (FAL 1 % sodium dodecylsulfate and 1 % 2-mercaptoethanol Braunschweig, F.R.G.), Polyporus obtusus (ATCC no. for 2 h at 50 "C before the run. The following reference 26733), which produces alcohol oxidase, was used as proteins, with their molecular weights given, were a fungus belonging to the white rot fungi [7]. The used: trypsin inhibitor from soybean, 21 500; bovin fungi were grown in 500-ml conical flasks containing serum albumin, 68000; RNA polymerase from E. coli 100 ml of the medium : 0.4 % (w/v) yeast extract, 1.O % and its subunits, 39000, 155000, 165000 [14-161. (w/v) malt extract and 0.4 76 (w/v) glucose. The flasks were inoculated by a mycelial suspension and incu- Ultracen tvijiuga t ion bated at 27 "C on a rotary shaker (100 rev./min) for 9 days (Poria contigua), for 15 days (Lenzites trabea) Sedimentation equilibrium ultracentrifugations or for 20 days (Polyporus obtusus). Mycelia were were performed in a Beckman Spinco model E analyti- harvested by filtration, washed with 50 mM potassium cal ultracentrifuge equipped with monochromator and phosphate buffer, pH 7.5, and stored at - 20 "C until photoelectric scanner. The enzyme was dissolved in required for use. 10 mM potassium phosphate buffer, pH 7.6. Protein The yeasts Candida boidinii (ATCC 32 195) and concentration was measured by absorbance at 280 nm. Hansenulu polymovpha (CBS 4732) were grown in a basal medium with 1 (v/v) methanol as the sole % Immunological Assays carbon and energy source as described previously [8]. Antibodies against alcohol oxidase were raised in a rabbit by subcutaneous injection of purified enzyme Assay of Alcohol Oxidase (2.3 mg) dissolved in 1 ml of 50 mM potassium phos- The enzyme activity was measured at 30'C and phate buffer, pH 7.5, together with 1 ml of Freund's with air-saturated solutions by determination of complete adjuvant and 0.2 ml of 9% NaCl solution. hydrogen peroxide production or oxygen consump- Two following injections (1.9 mg) were given at weekly tion; both assays gave comparable results. The for- intervals. The animal was bled from the ear vein. mation of hydrogen peroxide was determined by modi- Serum was stored at - 20 "C. fication of the method of Sahm and Wagner [9]. The Double immunodiffusion tests were conducted in assay mixture consisted of: 50 pmol potassium phos- 2 % agarose gels with a 0.1 M Tris-HC1 buffer, pH 7.5, phate buffer, pH 7.5, 100 pmol methanol, 2 pmol 2,2'- containing 0.005 % merthiolate [17]. Immunoelectro- azino-bis(3-ethylbenzthiazoline 6-sulfonate), 3 units phoresis was carried out on agarose electrophoresis of peroxidase and limiting amounts of enzyme in a films (Corning ACI, California, U.S.A.) using a total volume of 1 ml. The increase in absorbance at 0.05 M barbital buffer, adjusted to pH 8.6 with HCl; 420 nm was followed [lo]. 15 V/cm were applied for 30 min. Oxygen consumption was measured in an oxygen electrode cell (Yellow Springs Instrument Co., Inc., Other Analytical Methods U.S.A.). The reaction mixture was composed of 150 pmol potassium phosphate buffer, pH 7.5, Protein was determined by the method of Lowry 300 pmol methanol and limiting amounts of enzyme et al. [18], using bovine serum albumin as a standard. in a total volume of 3 ml. One unit of alcohol oxidase The prosthetic group (FAD) was identified in the activity is defined as the amount of enzyme producing enzyme extract after 2-min treatment at 100°C by 1 pmol hydrogen peroxide, or consuming 1 pmol thin-layer chromatography (silica gel 60). The solvent oxygen per min under assay conditions. systems were the same as described by Pazur and Kleppe [19]. The FAD in the enzyme extract was determined by measurement of the oxygen consump- Polyacvylumide Gel Electrophoresis tion using apo-D-amino acid oxidase [20]. Formal- Analytical and preparative polyacrylamide gel dehyde formed in the reaction mixture was assayed electrophoresis were performed in 7% slab gels. The by the chromotropic acid reaction as described by separation gels contained in a final concentration Frisell and Mackenzie [21]. Iron analysis was per- 0.375 M Tris-HCI buffer, pH 8.9, according to system 1 formed with bathophenanthroline [22], as well as by of Maurer [13]. The gels were stained with Coomassie atomic absorption and emission spectroscopy mea- brilliant blue as described by Fairbanks et al. [12]. For surements. For electron microscopic analysis, the S. Bringer, B. Sprey, and H. Sahm 565 enzyme was applied to a carbon-coated copper grid, ugation and the extraction procedure was repeated. negatively stained with 2% uranyl acetate, and exa- The combined supernatant fractions were dialyzed mined in a Siemens Elmiskop I electron microscope. against 50 mM potassium phosphate buffer, pH 7.5 Plates were exposed at a primary magnification of and concentrated by ultrafiltration. Data of a typical 80000 x . For amino acid analysis, the enzyme was purification experiment are presented in Table 1. The hydrolyzed at 110 "C for 20 h in evacuated, sealed purified enzyme gave a single band after disc gel elec- Pyrex tubes. The hydrolyzate was analyzed in a Beck- trophoresis, and sedimented as a single component in man Multichrom amino acid analyzer. the ultracentrifuge. Step 3b : Sucrose Gradient Centrifugation. Since the molecular weights of the alcohol oxidases isolated RESULTS from yeasts were found to be very high, we also tried to isolate the enzyme by sucrose density gradient Purification of Alcohol Oxidase centrifugation as described by Goldthwaite and Bogo- Unless otherwise stated, all operations were carried rad [23].

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