Solubilization and Activation of Membrane-bound Acid Protease of Aspergillus oryzae

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1 Agric. Biol. Chem., 41 (11), 2125 `2130, 1977 Solubilization and Activation of Membrane-bound Acid Protease of Aspergillus oryzae Yoshio TSUJITA and Akira ENDO Fermentation Research Laboratories Sankyo Co., Ltd., Hiromachi, Shinagawa-ku, Tokyo 140, Japan Received March 22, The membrane-bound acid protease of Aspergillus oryzae was solubilized by treat ments with snail gut extract and phospholipase A, and with several detergents including Triton X-100, Tween 80, and cholic and deoxycholic acids. Other hydrolytic enzymes tested were not effective in the solubilization of enzyme. 2. Membrane-bound acid protease was activated with lipid mixture extracted from membrane fraction of A. oryzae as well as with detergents. Acid protease of Aspergillus oryzae is pro duced extracellularly on both solid bran and liquid cultures. The enzyme produced on wheat bran culture is composed of two distinct molecular forms, one of which is devoid of carbohydrate and the other is associated with carbohydrate with polysaccharide nature.1,2) When A. oryzae is grown in liquid medium, in addition to acid protease excreted into culture medium,3) substantial amounts of the enzyme activity are located within the cells.4) A part of the intracellular acid protease is recovered in the soluble fraction after mech anical disruption of cells, and the rest of the activity in the membrane mixture.4) The membrane-bound acid protease is solubilized and activated with Triton X-100.4) In the present paper, solubilization of membrane-bound acid protease with various treatments and its activation with Triton X-100 and membrane lipids were studied. The results indicate that two enzyme preparations, snail gut extract and phospholipase A, were effective in the solubilization of the enzyme as well as some detergents and that Triton X-100 and lipid mixture extracted from membrane fraction of A. oryzae activated the enzyme approximately 4- and 3-fold, respectively. MATERIALS AND METHODS Materials. Lysozyme (egg white, crystallized three times), ƒà-glucuronidase (Escherichia coli, type I; bovine liver, type B-1; Patella vulgata, type L-1), chitinase (Streptomyces griseus, 2 `3 units per mg dry weight), ƒ -glucosidase (Saccharomyces cerevisiae, type I), ƒàglucosidase (almonds), trypsin (bovine pancreas, twice crystallized), phospholipase C (Clostridium welchii, type I), phospholipase D (cabbage, type 1) and lysoleci thin (egg yolk, 98% purity) were obtained from Sigma Co. (U.S.A.). Cellulase (Trichoderma viride, purity 95%) and lipase (Rhizopus delemer, pure grade) were purchased from Seikagaku Kogyo Co. (Tokyo, Japan). Phospholipase A (Crotalus terrificus terrificus venom, 200 units per mg protein) was purchased from C. F. Boehringer & Soehne GmbH Mannheim (West Ger many), snail gut extract 'Glusulase' (Helix pomatia) from Endo Laboratories, Inc. (New York, U.S.A.), and Pronase P (Streptomyces griseus, crude enzyme powder) from Kaken Kagaku Co. (Tokyo, Japan). BIO-SIL BH (silicic acid for lipid chromatography, 100 `200 mesh), and Bio-Gel A-15m (200 `400 mesh) were obtained from BIO-RAD Laboratories (California, U.S.A.). Silica gel Plates for thin-layer chromatography (Kieselgel F254), and hammarsten milk casein were from E. Merck (West Germany). Enzyme assay. Proteolytic activity against casein was determined by a modified Anson's method as described previously.1) The reaction mixture (150ƒÊl) contained 2 `20 units of the enzyme and 1 mg of milk casein in citric acid/phosphate buffer (26.5mm citric acid/13.7 mm Na2HPO4), ph 3.0. Incubation was conducted at 37 Ž for 10min and reaction was termi nated by the addition of 150ƒÊl of 10% trichloroacetic acid. After standing for 20min at 37 Ž, the precipitate formed was removed by filtration, and the resultant

2126 Y. TSUJITA and A. ENDO filtrate (200ƒÊl) was taken to determine the amount of trichloroacetic acid-soluble products, using Folin- Ciocalteau phenol reagent.

2 2126 Y. TSUJITA and A. ENDO filtrate (200ƒÊl) was taken to determine the amount of trichloroacetic acid-soluble products, using Folin- Ciocalteau phenol reagent.5) One unit of acid protease activity was defined as the amount of enzyme that developed the color equivalent to 1 ƒêmole of tyrosine per min under the conditions described above. Protein. Protein concentration was measured by the method of Lowry et ƒ l.6) Preparation of membrane fraction from mycelia of A. oryzae. A. oryzae (365-U-64-1) was grown for 65hr at 28 Ž in 500-m1 Sakaguchi flasks containing 100ml of culture medium as described previously.5) The mycelia were harvested by filtration and then washed 5 times with cold saline (4 Ž, 0.9%. NaCI). The mycelial mat from 20 flasks (wet weight 120g) was ground in a mortar with silica sands (4060 mesh, 3g/g of wet mycelia) at 0 Ž and then extracted with 4 volumes of 50mm sodium acetate buffer, ph 5.8, containing 5mm MgCl2, 0.5mm EDTA and 0.25M RESULTS AND DISCUSSION Solubilization Among various hydrolytic enzymes tested, snail gut extract was the most effective in the solubilization of membrane-bound acid pro tease (Table I, exp. 1). Phospholipase A was somewhat lesser effective than snail gut ex tract. Lysozyme, cellulase, phospholipases C and D and ƒà-glucuronidase of E. coli solu bilized the membrane enzyme to a slight extent. Other enzymes tested were ineffective (Table I, exp. 1). All detergents tested in cluding both nonionic and anionic ones were highly effective in the solubilization of the membrane-bound acid protease and 2-mer captoethanol were somewhat lesser effective sucrose. The mixture was centrifuged at 500 ~g for 5min and the supernatant solution was then centrifuged at 105,000 ~g for 120min. The pellet obtained after centrifugation at 105,000 ~g was washed twice with the above mentioned buffer and used as membrane fraction. Under these conditions, acid protease acti vity contained in membrane and soluble fractions (105,000 ~g supernatant) was 15.2 and 84.8%, respec tively, of total cell-bound activity. Delipidated membrane-bound acid protease. To 5ml of 0.7% Triton X-100 solution (in saline), was added 1 ml of the suspension of membrane fraction obtained above (10mg protein/ml of saline). The mixture was gently shaken at 37 Ž for 60min and then centrifuged at 105,000 ~g for 60min. The resultant supernatant was mixed with 2 volumes of cold acetone (-20 Ž) and the precipitate formed was collected by centrifugation at 10,000 ~g for 10min, followed by washing twice with cold acetone. This precipitate, designated as delipidated membrane-bound acid pro tease, was suspended in saline and used. Delipidated membrane fraction and membrane lipids. Membrane fraction (990mg protein suspended in 98ml of saline) was added to 20 volumes of cold ethanol-diethylether (3:1, -20 Ž) with vigorous stirring, and the mixture was centrifuged at 10,000 ~ g for 10 min at -20 Ž. The pellet was washed twice with 2000ml of the same solvent mixture and, after dried in vacuo, used as delipidated membrane fraction (968mg). The supernatant solution and washings obtained above were combined and evaporated to dryness under reduc ed pressure, giving 1.13g of membrane lipids. FIG. 1. Solubilization of Membrane-bound Acid Protease with Phospholipase A. A. Membrane fraction (2mg protein) was suspended in 0.5ml of saline containing 0.02% (w/v) of phos pholipase A and the mixtures were incubated with shaking at 37 Ž for various periods of time. B. Membrane fraction (2mg protein) was suspended in 0.5ml of saline containing various amounts of phospholipase A and the mixtures were incubated for 60min as described above. After incubation the mixtures (from both A and B) were centrifuged at 105,000 ~g for 60min and the resultant pellet ( œ--- œ) and supernatant solution ( \ ) were assayed for acid protease activity as described in MATERIALS AND METHODS.

3 A. oryzae Membrane Acid Protease 2127 TABLE I. SOLUBILIZATION OF MEMBRANE-BOUND ACID PROTEASE OF A. oryzae BY VARIOUS TREATMENTS The incubation mixture (0.5ml) containing 0.9% sodium chloride, 1mg (protein) of membrane frac tion and an enzyme and/or chemical was gently shaken at 37 Ž for 60min and then centrifuged at 105,000 ~g for 60min. The pellet obtained was washed once with saline. Aliquots of both resultant supernatant solution and the pellet were assayed for acid protease activity as described in MATERIALS AND METHODS. a) (i) From E. coli, (ii) bovine liver and (iii) Patella vulgata, respectively. b) Incubation mixture contained 1 % methanol. (Table I, exp. 2). Lysolecithin had no effect on the extraction of the membrane acid pro tease, indicating that the solubilizing activity of phospholipase A does not result from the detergent action of lysolecithin which was possibly produced by the hydrolysis of mem brane phospholipid during incubation. In most cases, enzyme activity recovered in the soluble fraction (supernatant) was over 100% to that of the original membrane fraction. As shown in Fig. IA and 1B, the amount of acid protease which was solubilized with phospholipase A was at most 70% of the total activity associated with membrane frac tions under various conditions where incuba tion times and concentrations of phospholi pase A were varied. When the phospholipase A-solubilized fraction was submitted to gel filtration in the absence of Triton X-100, one active peak corresponding to M24) was ob tained (Fig. 2A). Acid protease Ml was then solubilized from the residue remaining after

4 2128 Y. TSUJITA and A. ENDO standard assay procedure (in the absence of Triton X-100); œ \ œ, acid protease activity determined in the presence of 0.7% Triton X-100; ---, protein. phospholipase treatment with Triton X-100 (Fig. 2B), indicating that phospholipase A is effective in the extraction of acid protease M2 alone. Solubilization of acid protease by treatment with Triton X-100 depended on its concentra tion. At concentrations higher than 0.7% of Triton X-100, almost all acid protease activity bound to membrane fraction was solubilized (Fig. 3) and the recovery of FIG. 2. Gel Filtration on Bio-Gel A-15m of Mem brane-bound Acid Proteases Which were Solubilized by Successive Treatments with Phospholipase A (A) and Triton X-100 (B). Membrane fraction (7.2mg protein; 42 units of acid protease) was suspended in 5ml of saline containing 1mg (protein) of phospholipase A and the mixture was incubated with stirring at 37 Ž for 60min, followed by centrifugation at 105,000 ~g for 60min. The supernatant solution was concentrated to a small volume with a membrane filter (Diafilter G-10T, Bioengineering Co., Tokyo). A. A portion of the concentrated fraction (4.7mg protein, 21.3 units of acid protease) was applied to a column of Bio-Gel A-15m (1.52 ~55cm) equilibrated with 50mm acetate buffer, ph 5.2. The column was then developed with the same buffer and fraction of 3ml were col lected at a flow rate of 5ml/hr. B. The pellet ob tained after 105,000 ~g centrifugation in A (3.5mg protein, 20 units of acid protease) was washed once with 2ml of saline and suspended in 5ml of saline containing 0.7% Triton X-100. The mixture was incubated with shaking at 37 Ž for 60min and then centrifuged at 105,000 x g for 60min. To the resul tant supernatant (4.8ml) was added 9.6ml of cold acetone (-20 Ž) with stirring and the precipitate formed was collected by centrifugation at 10,000 ~g for 10min and then washed with 5ml of 70% acetone. A portion of the pellet thus obtained (2.4mg protein, 0.7 units) was suspended in 50mm acetate buffer, ph 5.2 and then submitted to gel filtration as described above. \, acid protease activity determined by FIG. 3. Solubilization of Membrane-bound Acid Protease with Triton X-100. Membrane fraction (2mg protein) suspended in 0.5ml of saline was incubated with Triton X-100 at varying concentrations with shaking at 37 Ž for 60min and the mixture was then centrifuged at 105,000 ~g for 60min. The resultant pellet ( œ--- œ) and supernatant solution ( - ) were measured for acid protease activity as described in MATERIALS AND METHODS. activity was over 200%, When delipidated membrane-bound acid protease was incubated in the presence of 0.7% Triton X-100, the enzyme was activated over 4-fold. As reported previously,4) the solubilized fraction obtained after Triton X-100 treatment gave 2 active peaks (M1 and M2) on gel filtration (data not shown). As described in MATERIALS AND METHODS, membrane fraction used in this study is the pellet obtained by centrifugation of disrupted mycelia at 500 `105,000 ~g and hence ap parently consists of mitochondria, microsomes

5 and some other membraneous structures. The localization of these active peaks (M1 and M2) in the cell is under investigation and will be reported elsewhere. Activation with membrane lipid Extraction of membrane fraction with ethanol-diethylether (3:1) causes a 60 reduction in the activity of acid protease. Enzyme activity associated with this delipi dated membrane fraction was activated by adding back membrane lipids (Fig.4). The A, oryzae Membrane Acid Protease 2129 FIG. 5. Thin-layer Chromatograms of Membrane Lipid Fractions Obtained by Silica Gel Chromato graphy. Membrane lipids (625mg, obtained as described in MATERIALS AND METHODS) were applied to a BIO SIL BH column (3 ~8.5cm) equilibrated with chloro form. The column was first washed with 550ml of chloroform and then successively developed with chloroform-methanol mixtures in varying ratios (9:1; 8:2; 7: ; 6:4; 4:6). Volumes of each mixture ap FIG.4. Activation by Membrane Lipids of Acid Protease Associated with Delipidated Membrane Frac tion. To test tubes (8 ~105mm), were added 24 ~28ƒÊl of water, varying amounts of membrane lipids (obtained as described in MATERIALS AND METHODS) suspended in 2 `6ƒÊl of methanol and 20ƒÊl (5.2ƒÊg protein) of delipidated-membrane acid protease (obtained as described in MATERIALS AND METHODS) in this order (total volume, 50ƒÊl) at 0 Ž, and the mixtures were preincubated at 37 Ž for 5min. Then reaction was started by adding 100ƒÊl of 1% milk casein dissolved plied were 500ml. Eluates were separately pooled and evaporated to dryness under reduced pressure. Yields of lipid(s) from each eluate are shown in the figure. Approximately 30ƒÊg of each lipid fraction was applied to thin-layer chromatography in chloro form-methanol-water (65:25:4). Lipids were visua lized with iodine vapor. TABLE II. ACTIVATION OF DELIPIDATED MEMBRANE- BOUND ACID PROTEASE WITH MEMBRANE LIPID FRACTIONS OF A. oryzae Experimental conditions were the same as those in Fig. 4, except that total lipid used were 100ƒÊg per assay. in citric acid/phosphate buffer (26.5mM citric acid/ 13.7mm Na2HP04), ph 3.0. maximum specific activity was obtained at 100ƒÊg or more lipids per assay. To determine lipid(s) effective in the acti vation of membrane-bound acid protease, membrane lipids (625mg) were submitted to silica gel chromatography and separated into 6 fractions (Fig. 5). All lipid fractions obtain ed except fraction 1 activated acid protease bound to delipidated membrane by 30 `48% (Table II). However, the highest activation a) Lipid fractions were mixed in the ratio shown in Fig. 5 (see yield of lipid(s)), and 100ƒÊg of the mixture was used. b) Membrane lipids obtained as described in MATERIALS AND METHODS.

6 2130 Y. TSUJITA and A. ENDO was obtained with lipid mixture which con tained all 6 fractions in the ratio similar to those in original membrane fraction. Thus, there was no particular lipid which was solely effective in the activation of membrane-bound acid protease. REFERENCES 1) Y. Tsujita and A. Endo, Biochim. Biophys. Acta, 445, 194 (1976). 2) Y. Tsujita and A. Endo, J. Biochem., 81, 1063 (1977). 3) Y. Tsujita and A. Endo, J. Bacteriol., 130, 48 (1977). 4) Y. Tsujita and A. Endo, Biochem. Biophys. Res. Commun., 74, 242 (1977). 5) O. Folin and V. Ciocalteau, J. Biol. Chem., 73, 627 (1927). 6) O. H. Lowry, N. J. Rosebrough, A. L. Farr and R. J. Randall, ibid., 193, 265 (1951).

Studies on the Glucanase of Sclerotinia libertiana. EBATA and Yukio SATOMURA

Studies on the Glucanase of Sclerotinia libertiana By Junko EBATA and Yukio SATOMURA Faculty of Science, Osaka City University, Osaka Received December 13, 1962 The digestion of yeast cells with the glucanase