Studies on the Polymorphism of l-Glutamic Acid

The effects on the polymorphic crystallization of l-glutamic acid were examined of many substances including amino acids, inorganic salts, surface active agents, and sodium salt or hydrochloride of l-glutamic acid, when contained in the mother liquor.

The co-existence of amino acids, especially of l-aspartic acid, l-phenylalanine, l-tyrosine, l-lcucine and l-cystine contributed to the crystallization of l-glutamic acid in α-form, and these amino acid showed an inhibitory action on the transition of α-crystals as the solid phase in the aqueous solution, to β-crystals.

In the presence of a large amount of l-glutamate or the hydrochloride at the time of nucleation of l-glutamic acid, mostly β-crystals appeared even in the presence of the amino acids named above.     

Regulation of l-Glutamate Biosynthesis by Copper Ions

A specific regulatory effect of copper ions on the microbiological synthesis of l-glutamate from acetate was found. The minimal concentration of copper ions necessary for the maximal production of l-glutamate was about 0.025 µg/ml at which the yield of l-glutamate was four times greater than that in the absence of copper ions. This effect of copper was demonstrated only when acetate was the substrate; it was not observed when the substrate was glucose ethanol, lactate or n-paraffin.

The physiological features of the l-glutamate production from acetate were examined in the presence or absence of copper ions. The most striking features of the culture without added copper ions were the increase in Q_O2 and NADH oxidase and the marked reduction of succinate oxidase accompanied with the reduction of l-glutamate formation. In addition, the regulation of l-glutamate synthesis by copper ions proved to have no relation to the wellknown regulatory factor, cell permeability. These facts suggest that the l-glutamate biosynthesis from acetate is regulated through unknown factors related to the respiratory activities.     

Alkaline Earth Salts of Glutamic Acid and Optical Resolution of their Racemic Modifications

The solubilities of monocalcium and monomagnesium diglutamate and calcium, magnesium, barium and strontium glutamate in water were measured in respect to both the l-form and the dl-form to conjecture the constitution of the racemic modification of each salt. It was concluded from the result that only magnesium dl-glutamate among six saltsis a congromerate and the others except the barium salt are all racemic compounds. The conclusion was supported by results from measurements of the infrared spectra and the X-ray diffractions. As for barium glutamate, a definite conclusion could not be obtained, but its racemic form seems to be congromerate or a racemic compound with a weak affinity between the isomers. Optical resolution based on the inoculation method was tried for calcium, magnesium, barium and strontium dl-glutamate, and the selective crystallization of the active form from the supersaturated solutions of magnesium and calcium dl-glutamate proceeded, though the process was unstable in the latter case; on the other hand, the resolutions of barium and strontium dl-glutamates were quite unsuccessful.     

Properties and Continuous Use of Microbial Fumarase Entrapped in Fibres

A new flavoprotein enzyme, l-glutamate oxidase, was purified to homogeneity from an aqueous extract of a wheat bran culture of Streptomyces sp. X-l 19–6. It showed absorption maxima at 273, 385 and 465 nm and a shoulder around 490 nm, and contained 2 mol of FAD per mol of enzyme. The enzyme had a molecular weight of approximately 140,000 and consisted of three sizes of subunits with molecular weights of 44,000, 16,000 and 9,000. Balance studies showed that 1 mol of l-glutamate was converted to 1 mol of α-ketoglutarate, ammonia and hydrogen peroxide with the consumption of 1 mol of oxygen. In addition to l-glutamate, l-aspartate was oxidized by the enzyme but only to an extent of 0.6% at pH 7.4; the Michaelis constants were as follows: 0.21 mM for l-glutamate and 29 mM for l-aspartate. The isoelectric point was pH 6.2, and the enzyme activity was optimal between pH 7.0 and 8.0. When the enzyme was heated at pH 5.5 for 15 min, the remaining activity was 100% of the original activity level at 65°C, 87% at 75°C and 47% at 85°C.     

Induction of Antibiotic Formation in Streptomyces sp. No. 362 by the Change of Cellular Fatty Acid Spectrum

Microorganisms which require oleic acid for the formation of antibiotics were screened. Streptomyces sp. No. 362, one of the selected organisms, produced antimicrobial substances only when oleic acid, palmitic acid or the high concentration of l-glutamic acid (or l-glutamine) was supplemented to the medium. The cellular fatty acid composition was changed by the supplement of these fatty acids, but not by l-glutamic acid (or l-glutamine). Antibiotic-producing cells had about 4 to 10 times larger amino acid pools, especially l-glutamic acid pool, and hexosamine pools. The ability for l-glutamate uptake of cells grown in the oleic or palmitic acid supplemented medium was markedly enhanced and the efflux of the accumulated l-glutamate was reduced. The antibiotic produced by this strain was identified as one of the streptothricin-group antibiotics and the role of these additives in the antibiotic formation is discussed.     

Glutamate Metabolism in a Glutamate-producing Bacterium,Brevibacterium flavum

Brevibacterium flavum No. 2247 was found to grow with l-glutamate as the sole carbon and nitrogen source on an agar-plate medium when high concentrations of l-glutamate, FeSO₄ and biotin were added to the medium. It grew on l-glutamate in liquid medium only when yeast extract or high concentrations of FeSO₄ and glucose or organic acids of the tricarboxylic acid cycle were added to the medium. The growth on l-glutamate in liquid medium was also stimulated by high concentrations of l-glutamate, biotin and MgSO₄, and inhibited by a high concentration of (NH₄)₂SO₄.

Aspartate aminotransferase (TA)- and α-ketoglutarate dehydrogenase (KD)-defective mutants did not grow on l-glutamate, and glutamate-utilizing revertants derived from these mutants recovered TA and KD activity, respectively, whereas glutamate dehydrogenase (GD)-defective mutants grew on l-glutamate. Washed cells of strain No. 2247 grown on glutamate decomposed the amino acid, whereas those grown on glucose did not. The degradation was observed only under aerobic conditions. The former cells showed higher KD, succinate dehydrogenase and fumarase activities than the latter cells. Of 75 mutants which did not grow on glutamate but grew on succinate, three strains lacked KD but showed the same glutamate productivity as the parent strain. Four other strains with normal KD levels showed higher glutamate productivity than the parent.     

Asymmetric synthesis of l-6-hydroxynorleucine from 2-keto-6-hydroxyhexanoic acid using a branched-chain aminotransferase

Abstract

l-6-Hydroxynorleucine was synthesized from 2-keto-6-hydroxyhexanoic acid using branched-chain aminotransferase from Escherichia coli with l-glutamate as an amino donor. Since the branched-chain aminotransferase was severely inhibited by 2-ketoglutarate, the branched-chain aminotransferase reaction was coupled with aspartate aminotransferase and pyruvate decarboxylase. Aspartate aminotransferase converted the inhibitory 2-ketoglutarate back to l-glutamate by using l-aspartate as an amino donor. On the other hand, pyruvate decarboxylase further shifted the reaction equilibrium towards l-6-hydroxynorleucine through decarboxylation of pyruvate to acetaldehyde. The concerted action of the three enzymes significantly enhanced the yield compared to that of branched-chain aminotransferase alone. In the coupled reaction, 90.2 mM l-6-hydroxynorleucine (> 99% ee) was produced from 100 mM 2-keto-6-hydroxyhexanoic acid, whereas in a single branched-chain aminotransferase reaction only 22.5 mM l-6-hydroxynorleucine (> 99% ee) was produced.     

Synthesis of γ-Glutamylpeptides by γ-Glutamylcysteine Synthetase from Proteus mirabilis

Syntheses of various γ-glutamylpeptides were examined taking use of the highly purified γ-glutamylcysteine synthetase from Proteus mirabilis. The accumulation of each peptide was measured after long time incubation, and good formation was observed in the synthesis of peptides of following amino acids, l-cysteine, l-α-aminobutyrate, l-serine, l-homoserine, glycine, l-alanine, l-norvaline, l-lysine, l-threonine, taurine and l-valine. Peptide syntheses were confirmed by analyses of the component amino acids, after hydrolysis of the peptides.

The structure of the glutamylpeptides, especially the peptide-linkage at the γ-carbonyl residue of l-glutamate, was determined by mass spectrometry of the N-trifluoroacetyl methylester derivatives of the glutamylpeptides. Enzymatic synthesis of γ-glutamyl-l-α-aminobutyrate was also confirmed by PMR spectrometry in the comparison with chemically synthesized compound.     

Separation of l-Leucine-pyruvate and l-Leucine-α-ketoglutarate Transaminases in Acetobacter suboxydans and Identification of Their Reaction Products

l-Leucine-pyruvate and l-leucine-α-ketoglutarate(α-KGA) transaminases were separated by DEAE-cellulose column chromatography and partially purified to 200- and 50-fold, respectively, from the cell-free extract of Acetobacter suboxydans (Gluconobacter suboxydans IFO 3172). The optimum pH range of the former was 5.0~5.5 and that of the latter was 8.5~9.0. l-Leucine, l-citrulline, and l-methionine were the most effective amino donors for the l-leucine-pyruvate transaminase. Basic amino acids as well as aromatic amino acids were able to be amino donors for the transamination with pyruvate. α-KGA was effective as an amino acceptor for this enzyme. The l-leucine-α-KGA transaminase had the typical properties of the branched-chain amino acid transaminase in its substrate specificity.

The reaction products of the transaminations were identified. l-Alanine was formed from pyruvate and l-glutamate from α-KGA. α-Keto acids formed from various amino acids by the l-leucine-pyruvate transaminase were also identified.     

Branched Chain Amino Acid Aminotransferase of Pseudomonas sp

Branched chain amino acid aminotransferase was partially purified from Pseudomonas sp. by ammonium sulfate fractionation, aminohexyl-agarose and Bio-Gel A-0.5 m column chromatography.

This enzyme showed different substrate specificity from those of other origins, namely lower reactivity for l-isoleucine and higher reactivity for l-methionine.

Km values at pH 8.0 were calculated to be 0.3 mm for l-leucine, 0.3 mm for α-ketoglutarate, 1.1 mm for α-ketoisocaproate and 3.2 mm for l-glutamate.

This enzyme was activated with β-mercaptoethanol, and this activated enzyme had different kinetic properties from unactivated enzyme, namely, Km values at pH 8.0 were calculated to be 1.2 mm for l-leucine, 0.3 mm for α-ketoglutarate.

Isocaproic acid which is the substrate analog of l-leucine was competitive inhibitor for pyridoxal form of unactivated and activated enzymes, and inhibitor constants were estimated to be 6 mm and 14 mm, respectively.     

Studies on the Behaviors of Impurities on the Crystallization of l-Glutamic Acid

The behaviors of impurities on the crystallizations of the free acid and the hydrochloride, monosodium, zinc, calcium and barium salts of l-glutamic acid were examined, and a tendency was recognized that coexisting impurities were apt to be taken into the crystals when the crystallization proceeded from the zwitterion, i.e., Glu.^± or The adsorption of l-tyro-sine was compared when l, d and dl-glutamic acid were crystallized with coexistence of l-tyrosine, and an effect of more or less extent of steric configuration on its behavior could be recognized.     

l-Glutamic Acid Fermentation with Molasses

Conditions suitable for the cell wall lysis of a l-glutamate-producing bacterium, Microbacterium ammoniaphilum, by egg white lysozyme were studied, in order to make clear the correlation of the fatty acid composition of the cellular fractions and the extracellular accumulation of l-glutamate,

The cell wall of a phage-resistant strain was recognized to be almost completely lyzed by the lysozyme.

Using this result, the relationship between the fatty acid composition of each fraction and extracellular accumulation of l-glutamate was investigated, and the following thesis was proposed: The extracellular accumulation of l-glutamate in large quantity took place when the molar ratio of saturated/unsaturated fatty acid in the cell membrane fraction was above 1.     

On the Mechanism of l-Prolyl Diketopiperazine Formation by Streptomyces

Since l-prolyl diketopiperazines, l-prolyl-l-valine anhydride and l-leucyl-l-proline anhydride, had been isolated from the culture filtrate of Streptomyces sp. S-580, the mechanism of l-prolyl diketopiperazine formation by Streptomyces has been studied. These two l-prolyl diketopiperazines were not formed from their constituent amino acids incubated with intact cell or cell free homogenate of this strain in buffered salt solution containing energy source. However, from milk casein, poly peptone or gelatin, the former two were components of the culture medium of this strain, hydrolyzed with the pure streptomyces-protease, these l-prolyl diketopiperazines were obtained (only from gelatin, glycyl-l-proline anhydride were obtained in addition to these two). Furthermore, in hydrolysis of some synthetic l-prolyl peptides with this enzyme, l-prolyl diketopiperazine formation were also studied, and as the result, glycyl-l-proline anhydride was obtained from glycyl-l-prolyl-l-leucine but no l-prolyl diketopiperazine was formed from l-prolyl-l-leucyl-glycine. From these evidences, the possible route of l-prolyl diketopiperazine formation by Streptomyces has been discussed.     

l-Glutamic Acid Fermentation with Molasses

The relation between oleate and biotin to the extracellular accumulation of l-glutamate in Microbacterium ammoniaphilum was studied. And it was suggested that oleate was the essential constituent for the bacterial cell structure, and, at the same time, it participated in the cellular permeability of l-glutamate. On the other hand, biotin was recognized to play a role on the synthesis of cellular fatty acid, mainly oleate and palmitate. Through the discussion above mentioned, the reason was made clear that biotin was not necessary for the bacterial growth or the extracellular accumulation of l-glutamate, if oleate had been added.     

Production of l-allose and d-talose from l-psicose and d-tagatose by l-ribose isomerase

l-ribose isomerase (L-RI) from Cellulomonas parahominis MB426 can convert l-psicose and d-tagatose to l-allose and d-talose, respectively. Partially purified recombinant L-RI from Escherichia coli JM109 was immobilized on DIAION HPA25L resin and then utilized to produce l-allose and d-talose. Conversion reaction was performed with the reaction mixture containing 10% l-psicose or d-tagatose and immobilized L-RI at 40 °C. At equilibrium state, the yield of l-allose and d-talose was 35.0% and 13.0%, respectively. Immobilized enzyme could convert l-psicose to l-allose without remarkable decrease in the enzyme activity over 7 times use and d-tagatose to d-talose over 37 times use. After separation and concentration, the mixture solution of l-allose and d-talose was concentrated up to 70% and crystallized by keeping at 4 °C. l-Allose and d-talose crystals were collected from the syrup by filtration. The final yield was 23.0% l-allose and 7.30% d-talose that were obtained from l-psicose and d-tagatose, respectively.     

Studies on the Synthesis of l-Amino Acids

l-Homoserine was prepared by the reduction of l-aspartic acid β-methyl ester with sodium borohydride in water solution without any racemization. The yield of l-homoserine was about 25% of the theoretical amount, and no product other than l-homoserine, l-aspartic acid and l-aspartic acid β-methyl ester was present in the reaction mixture. The low yield of l-homoserine was ascribed to the hydrolysis of the ester.

l-Azetidine-2-carboxylic acid could not be detected in the reaction mixture. In contrast with the reduction of l-glutamic acid γ-esters, the reduction of l-aspartic acid β-ester was not accompanied by the cyclization.     

Studies on the Reaction Conditions of DOPA Production with Alcaligenes faecalis.

The effects of several factors on the enzymatic production of 3,4-dihydroxyphenyl-l-alanine (DOPA) and 3,4-dimethoxyphenyl-l-alanine (DMPA) by transamination reaction were investigated using wet cells of Alcaligenes faecalis IAM 1015. In addition, some experiments for the cultural conditions for transaminase production were performed. DOPA and DMPA were obtained in 80 and 90% yields, respectively, using the mixture of l-glutamate and l-aspartate as amino donors. Accumulation of DMPA in the culture under the growing state of the bacteria was also confirmed.     

NMR Spectra of α- and γ-l-Glutamyl-αaminoisobutyric Acid and Some Related Compounds

Two methyl groups of α-l-glutamyl-α-aminoisobutyric acid which were equivalent in the acidic solution became unequivalent in the aqueous and basic solutions. Such an unequivalence of two methyl groups was not manifested in the cases of γ-l-glutamyl-α-aminoisobutyric acid, α- and γ-l-glutamylisopropylamide, N-glutaryl-α-aminoisobutyric acid and N-glutarylisopropylamine.     

Utilization of Hydrocarbons by Microorganisms

As already reported, Corynebacterium hydrocarboclastus S10B1 was able to accumulate a good deal of l-glutamate in a thiamine-deficient medium at the sole expense of n-alkanes, but unable to form l-glutamate in a thiamine-sufficient medium though an abundant cell growth was observed.

α-Ketoglutaric acid and dl-alanine were found to be produced in the same thiamine-deficient medium in which l-glutamate was accumulated. Both products formed from n-tetradecane by this organism were isolated from culture broth, purified and identified. The optimum concentration of thiamine in the culture medium was 3 to 5 µg per liter for their production. The maximum yields of α-ketoglutaric acid and dl-alanine reached 16 g and 1.5 g per liter in the calcium carbonate-added medium, respectively. However, the addition of more than 30 μg per liter of thiamine extremely repressed their accumulation.     

Absolute Configuration of (+)-1-Acetoxy-p-menth-3-one Isolated from Essential Oil of Mentha gentilis (L.)

The most effective electro-energizing fermentation (E-E F) conditions for l-glutamate (l-Glu) production by Brevibacterium flavum No. 2247 were determined. The adding of 0.01 mm neutral red at the beginning of cultivation was found most effective. A 1.5 V direct current was applied to the culture broth at 6~8 hr after inoculation in the cathode compartment, l-Glu was produced at 51.0 mg per ml, and this is about a 15 % increase in yield compared to the yield of the not electro-energizing (E-E) control (44.3 mg/ml).