PROCESS FOR PRODUCTION OF L-AMINO ACIDS

Abstract: L-amino acids are produced by means of an microbial en­ zyme system by treating a 5-substituted hydantoin or an N-­ carbamyl derivative of an amino acid with cells or the con­ tents of cells of a strain which belongs to the genus Arthro­ bacter and which is capable of converting the 5-substituted hydantoin or N-carbamyl derivative into a corresponding L-­ amino acid.

Description: This invention relates to a microbial process for the production of L-amino acids, especially from 5-substituted hydantoins or N-carbamyl derivatives of amino acids using microbial enzymes. There have been proposed microbial processes for producing L-amino acids from 5-substituted hydantoins using various microbial enzyme Sources (see JP-B-l3850/67, JP-B-2274/79 and JP-B-8749/79). However, these processes are unsatisfactory from the efficiency viewpoint. There has also been known a process for producing L-methionine from DL-N-carbamylmethionine using a microbial enzyme (see JP-B-29678/80). This process requires separation of L-methionine from D-N-carbamylmethionine which remains in the reaction mixture, and accordingly is not sufficiently effective. The present inventors have now found that certain microbial strains belonging to the genus Arthrobacter are capable of effectively converting 5-substituted hydantoins into L-amino acids. The present invention provides a process for producing an L-amino acid in which a 5-substituted hydantoin or an N-carbamyl derivative of an amino acid is treated with cells or the contents of cells of a strain which belongs to the genus Arthrobacter and which is capable of converting the 5-substituted hydantoin or N-carbamyl derivative into a corresponding L-amino acid, characterised in that the strain is Arthrobacter sp. DK-200 [FERM P-7472 (FERM BP-730)] or a functionally equivalent mutant or a functionally equivalent genetically engineered variant thereof. The present invention also provides a culture in a culture medium, comprising a source of assimilable carbon, a source of assimilable nitrogen and inorganic salts of a strain belonging to the genus Arthrobacter and being capable of converting a 5-substituted hydantoin or N-carbamyl derivative of an amino acid into a corresponding L-amino acid, the culture being substantially free of other microorganisms, characterized in that the strain is Arthrobacter sp. DK-200 [FERM P-7472 (FERM BP-730)] or a functionally equivalent mutant or functionally equivalent genetically engineered variant thereof. The present invention further provides a strain belonging to the genus Arthrobacter and being capable of converting a 5-substituted hydantoin or N-carbamyl derivative of an amino acid into a corresponding L-amino acid, characterized in that the strain is Arthrobacter sp. DK-200 [FERM P-7472 (FERM BP-730)] or a functionally equivalent mutant or functionally equivalent genetically engineered variant thereof. The Arthrobacter strain is capable of converting 5-substituted hydantoins and/or N-carbamyl derivatives of L-, D- or DL-amino acids into the corresponding L-amino acids. Arthrobacter sp. DK-200 has been isolated by the present inventors. The strain Arthrobacter sp. DK-200 was deposited on February 27, l984 at the Fermentation Research Institute, Agency of Industrial Science and Technology, Ministry of International Trade and Industry, l-3, Higashi l-chome Yatabe-machi Tsukuba-gun Ibaraki-ken 305, JAPAN, and was assigned the FERM P accession number 7472, which corresponds to FERM BP-730. The taxonomical characteristics of the strain Arthrobacter sp. DK-200, FERM P-7472 (FERM BP-730), are as follows: l. Morphological properties: 0.3-0.5 x 0.8-5.0 micrometers cell size, polymorphic, not motile, no flagellum, no spore, negative or slightly positive in Gram staining but having gram-positive granules, and not acid-fast; 2. Growth properties in culture media: Nutrient agar plate culture; pale white, circular, convex and entire colonies; Nutrient agar slant culture; moderate growth, glossy, and filamentous; Nutrient liquid culture; uniformly turbid, precipitating, and no particular growth on the liquid surface; Nutrient gelatin stab culture; liquefying; 3. Physiological properties: nitrates not reduced, positive in denitrification, negative in MR test, negative in VP test, indole not produced, hydrogen sulfide not produced, starch not hydrolyzed, citric acid not utilized in either Koser medium nor Christensen medium, both nitrates and ammonium salts utilized, pigment not produced, negative in urease activity, negative in oxidase activity, positive in catalase activity, aerobic, growth at a temperature in the range of l7.8-33.2°C and a pH in the range of 5-l0, oxidative in OF test, lysine as dibasic amino acid in cell wall and not containing meso-diaminopimelic acid and arabinose, positive in DNase activity, positive in casein-hydrolysis, and growth on 2% NaCl and weak growth on 5% NaCl; Generation of acid and gas from sugars: Assimilation of hydrocarbons; According to Bergey's Manual of Determinative Bacteriology, 8th Ed. (l974), strain DK-200 belongs to the genus Arthrobacter on the basis of its taxonomical characteristics: that is, (l) polymorphic, (2) gram-positive granules contained in the cell, and (3) lysine contained in the cell wall and no meso-diaminopimelic acid nor arabinose contained in the cell wall. The strain DK-200 of the invention belongs to new species of the genus Arthrobacter since its taxonomical properties are distinct from those of any known species. The strain DK-200 may be prepared in large quantities by any conventional aerobic liquid culture in a medium containing a carbon source, a nitrogen source, inorganic salts and a small amount of organic nutrients which can be assimilated by the strain. The enzyme activity can be enhanced by an addition of a small amount of for example L-carbamyltryptophan to the culture medium. The culture may be carried out at a pH of from 4-ll and a temperature of from l5-40°C for a time of from 5-l20 hours. The thus obtained culture containing the cells is preferably used in the invention. In addition there can also be utilized treated materials of the cells, such as frozen cells, lyophilized cells, sonicated cells, and cell debris, e.g. homogenates and extracts of the cells, as well as intact cells. Furthermore, any variant having improved activity by some variation treatment can of course be used effectively in the present invention. Examples of 5-substituted hydantoins which can be used as starting materials in the invention include 5-benzylhydantoin, 5-indolylmethylhydantoin and 5-(4-hydroxybenzyl)-hydantoin. Examples of N-carbamyl derivatives of amino acids include N-carbamylphenylalanine, N-carbamyltryptophan and N-carbamyltyrosine. These starting materials may be in D, L or DL from. The starting materials are known or may be prepared in any conventional manner. For example, DL-N-carbamyl derivatives may be prepared by the reaction of DL-amino acids with potassium cyanide, or by the hydrolysis of DL-hydantoin derivatives of amino acids under appropriate conditions. In the process of the invention, there is preferably used 0.l-40%, more preferably l-l0% by weight of the 5-substituted hydantoin or preferably 0.l-50% by weight of the N-carbamyl derivative of an amino acid in the reaction mixture. The reaction of the invention may be conveniently carried out at a pH of from 4 to ll, preferably from 6 to 9. Reaction conditions outside these ranges are inefficient in practice in view of the enzyme activity and stability. The pH may vary as the reaction proceeds and, accordingly, the pH should be maintained at a desired value by the addition of an appropriate neutralizing agent. The reaction temperature may be from l5 to 50°C. In addition, a small amount, e.g. 0.l-l0 mM, of a metal ion, provided by compounds such as MnCl₂ and CoCl₂ will give better results. The L-amino acid produced can be separated from the reaction mixture, for example by centrifuging the mixture to remove insolubles such as the cells, passing the supernatant through a strong acid-H⁺ type cation-exchange resin to adsorb the L-amino acids followed by elution with aqueous ammonia, and further concentrating and cooling to deposit crystals. According to the present invention, L-amino acids can be produced very efficiently from 5-substituted hydantoins or N-carbamyl derivatives of amino acids, irrespective of the D-, L- or DL-form of the starting materials. The invention is now further described in the following Examples. In these Examples, the percentages are by weight unless otherwise noted. EXAMPLE l : A medium containing 0.5% glucose, 0.2% yeast extract, 0.l% disodium hydrogenphosphate, 0.05% potassium dihydrogenphosphate and 0.05% magnesium sulfate, having a pH of 7.5, was distributed into a number of test tubes and sterilized at l20°C for l5 minutes. DL-N-carbamyltryptophan which had also been sterilized was added to each test tube to provide a final concentration of 0.05%. Arthrobacter sp. DK-200 was then inoculated into the medium and cultured while shaking at 30°C for 24 hours. To the cultured medium there was added each of the 5-substituted hydantoins listed in Table l below. Shaking of the culture was further continued at 30°C for 24 hours. After reaction the cells were removed by centrifugation. Amino acids in the supernatants were quantitatively analyzed by HPLC and a bioassay using Lactobacillus arabinosus (ATCC No. 80l4). Based on the results of both analyses, each product was identified as the L-amino acids shown in Table l. EXAMPLE 2 : Into a 500 ml flask there was added 100 ml of a medium containing 0.5% glucose, 0.2% yeast extract, 0.l% disodium hydrogenphosphate, 0.05% potassium dihydrogenphosphate, 0.05% magnesium sulfate and 0.l% DL-5-indolylmethylhydantoin, having a pH of 7.5. The flask was sterilized at l20 C for l5 minutes. To the flask there was inoculated 5 ml of a seed culture of Arthrobactor sp. DK-200 which had been cultured at 30°C for 20 hours in a medium, having a pH of 7.5, containing 0.5% glucose, 0.5% yeast extract, 0.5% polypeptone and 0.5% sodium chloride. After 24 hour culture at 30°C, the cells were separated from the culture medium by centrifugation and washed once with saline. The cells were suspended in l00 ml of 0.l M Tris HCl buffer, having a pH of 7.0, containing 0.2 M DL-5-benzylhydantoin and 0.5 mM cobalt chloride, and incubated at 35°C for 65 hours. After reaction the cells were removed by centrifugation. The supernatant was concentrated to 20 ml and cooled to deposit crystals. The crystals were analyzed by TLC, HPLC, NMR and polarimetry and data corresponding to a standard specimen of L-phenylalanine were obtained as shown in Table 2. EXAMPLE 3 : Cells obtained in the same manner as Example l were suspended in 2 ml of 0.l M Tris HCl buffer, having a pH of 7.5, containing 0.5 mM cobalt chloride and l mM manganese chloride. The suspension was subjected three times to ultrasonication at 20 kHz for 3 minutes while cooling in an ice bath. D-5-benzylhydantoin was added (0.l M) to the suspension containing the cell debris, which was then incubated at 35°C for 40 hours. After reaction insolubles were centrifuged out, L-phenylalanine was obtained from the supernatant with a yield of 82%. Identities of the product were confirmed by HPLC and bioassay. EXAMPLE 4 : A medium, having a pH of 7.0, containing 0.5% glucose, 0.2% yeast extract, 0.l% disodium hydrogenphosphate, 0.05% potassium dihydrogenphosphate and 0.05% magnesium sulfate, was distributed into a number of test tubes in an amount of 5 ml in each test tube, and sterilized at 120°C for l5 minutes. DL-N-carbamyltryptophan, which had also been sterilized, was added to each of the tubes to provide a final concentration of 0.l%. Arthrobacter sp. DK-200 was then inoculated into the medium and incubated at 30°C for 24 hours with shaking. Cells collected from the medium by centrifugation were washed with the same amount of saline and suspended in 5 ml of 0.l M Tris HCl buffer, having a pH of 7.5, containing 0.l mM manganese chloride and 0.l M L-N-carbamylamino acid, each of which is listed in Table 3 below. The reaction was carried out at 35°C for 20 hours. Quantitative measurements of the products by bioassay with Lactobacillus arabinosus , ATCC No. 80l4, and HPLC were performed and the results are shown in Table 3. As shown in Table 3, the obtained products were identified as the corresponding L-amino acids. EXAMPLE 5 : Cells which had been obtained by the same manner as in Example 4 except for using 500 ml Erlenmeyer flasks containing l00 ml of the medium were suspended in l00 ml of 0.l M Tris HCl buffer, having a pH of 7.0, containing 0.l M D-N-carbamylamino acid listed in Table 4 below, 0.5 mM cobalt chloride and l mM manganese chloride, and incubated at 35°C for 60 hours. HPLC analysis of the reaction mixture showed that the reaction had been almost completed in this procedure. After centrifugation to remove the cells, the supernatant was concentrated to 25 ml, and about 5 ml ethanol was added and cooled to 5°C to deposit crystals. The crystals were recrystallized and analyzed by HPLC, TLC, bioassay, NMR and polarimetry. Comparisons of the obtained data with those of standard specimens of the corresponding L-amino acids confirmed the identities of the products shown in Table 4. EXAMPLE 6 : The procedures of Example 5 were repeated except that D-N-carbamylamino acids were replaced by DL-N-carbamylamino acids. The analysis results of the obtained products corresponded with those of standard specimens, as shown in Table 5. EXAMPLE 7 : Cells obtained in the same manner as in Example 5 were suspended in 20 ml of 0.l M Tris HCl buffer, having a pH of 7.0, containing 0.5 mM cobalt chloride and l mM manganese chloride. The suspension was subjected three times to ultrasonication at 20 kHz for 3 minutes under cooling in an ice bath. DL-N-carbamylamino acid was added to the cell debris solution in a concentration of 0.l M and incubated at 30°C for 20 hours. After reaction insolubles were removed by centrifugation, the resulting supernatant was analyzed by HPLC and bioassay. The products were identified as corresponding L-amino acids on the basis of the results of the analyses shown in Table 6.

Claims: A process for producing an L-amino acid in which a 5-substituted hydantoin or an N-carbamyl derivative of an amino acid is treated with cells or the contents of cells of a strain which belongs to the genus Arthrobacter and which is capable of converting the 5-substituted hydantoin or N-carbamyl derivative into a corresponding L-amino acid, characterized in that the strain is Arthrobacter sp. DK-200 [FERM P-7472 (FERM BP-730)] or a functionally equivalent mutant or functionally equivalent genetically engineered variant thereof. A process according to claim l, wherein the 5-substituted hydantoin is L-, D- or DL-5-benzylhydantoin and the L-amino acid is L-phenylalanine. A process according to claim l, wherein the 5-substituted hydantoin is L-, D- or DL-5-indolylmethylhydantoin and the L-amino acid is L-tryptophan. A process according to claim l, wherein the 5-substituted hydantoin is L-, D- or DL-5-(4-hydroxybenzyl)-hydantoin and the L-amino acid is L-tyrosine. A process according to claim l, wherein the N-carbamyl derivative is L-, D- or DL-N-carbamylphenylalanine and the L-amino acid is L-phenylalanine. A process according to claim l, wherein the N-carbamyl derivative is L-, D- or DL-N-carbamyltryptophan and the L-amino acid is L-tryptophan. A process according to claim l, wherein the N-carbamyl derivative is L-, D- or DL-N-carbamyltyrosine and the L-amino acid is L-tyrosine. A process according to any one of the preceding claims, wherein the cells are intact cells or disrupted cells. A process according to claim 8, wherein the intact cells are in culture. A process according to any one of claims l to 7 wherein the cells or the contents of cells are sonicated cells, frozen cells, lyophilized cells or a homogenate or extract derived from the cells. A process according to any one of Claims l to 7, wherein the 5-substituted hydantoin or N-carbamyl derivative is contacted with a culture of the said strain. A culture in a culture medium, comprising a source of assimilable carbon, a source of assimilable nitrogen and inorganic salts of a strain belonging to the genus Arthrobacter and being capable of converting a 5-substituted hydantoin or N-carbamyl derivative of an amino acid into a corresponding L-amino acid, the culture being substantially free of other microorganisms, characterized in that the strain is Arthrobacter sp. DK-200 [FERM P-7472 (FERM BP-730)] or a functionally equivalent mutant or functionally equivalent genetically engineered variant thereof. A strain belonging to the genus Arthrobacter and being capable of converting a 5-substituted hydantoin or N-carbamyl derivative of an amino acid into a corresponding L-amino acid, characterised in that the strain is Arthrobacter sp. DK-200 [FERM P-7472 (FERM BP-730)] or a functionally equivalent mutant or functionally equivalent genetically engineered variant thereof.

Inventors: CHIBA, SUSUMU DENKI KAGAKU KOGYO K.K., KATO, MASAAKI, KITAGAWA, HIRONOSHIN, MIYOSHI, TERUZO
Applicants: DENKI KAGAKU KOGYO KABUSHIKI KAISHA
Application year: 1985
Main classification: C12P13
IPC codes: C12P13