Antioxidant Effect of Peptide in Combination with Sugar on Autoxidation of Edible Oils

The antioxidant effect of various combinations of peptide and sugar was investigated by an oven-storage test using lard as substrate. High antioxidant activity was resulted from combining a peptides with branched-chain amino acids and xylose. For this effect, the presence of a branched-chain amino acid was more favorable at the N-terminal position of the peptide than at the C-terminal position. A synergistic effect was observable with xylose at a molar ratio of xylose-peptide of 0.05. The leucylglycine-xylose composition was also effective for preventing oxidation in selected vegetable oils.     

Enhancement of isoleucine hydroxamate-mediated growth inhibition and improvement of isoleucine-producing strains of Serratia marcescens.

Growth inhibition by isoleucine hydroxamate in Serratia marcescens was significantly enhanced by adding valine plus leucine and by using glycerol as the carbon source. Isoleucine hydroxamate-resistant mutants were isolated under conditions in which growth inhibition was enhanced. One of the mutants, strain GIHVLr2179, lacked both feedback inhibition and repression of threonine deaminase. An alpha-aminobutyric acid-resistant mutant derived from strain GIHVLr2179, strain GIHVLAr2795, produced 12 mg of isoleucine per ml in the medium containing glucose and urea as carbon and nitrogen sources (a twofold increase over prior reports). This strain had increased activities of threonine deaminase, acetohydroxy acid synthase, aspartokinase, and homoserine dehydrogenase.     

Stability of fumarase activity of Brevibacterium flavum immobilized with ϰ-carrageenan and Chinese gallotannin

Summary In order to improve L-malic acid productivity by Brevibacterium flavum immobilized with -carrageenan, addition of Chinese gallotannin to the immobilization medium was investigated. As the results show, the optimal concentration of Chinese gallotannin was 0.1% (w/v). Fumarase activity and the stability of this improved preparation were higher than in one with only -carrageenan. Addition of Chinese gallotannin was more advantageous to stability towards ethanol than addition of polyethyleneimine. The L-malic acid productivity of the immobilized cells at 37°C was 42.2 kg/h per 1,000 l column, and increased threefold compared with that of B. flavum immobilized with only -carrageenan, and was 25 times that of B. ammoniagenes immobilized with polyacrylamide. Persimmon tannin also increased the stability of fumarase.     

Improvement of production of l-aspartic acid using immobilized microbial cells

Summary In our laboratory, EAPc-7 a strain having higher aspartase activity was derived from Escherichia coli ATCC 11303. For the improvement of l-aspartic acid productivity using EAPc-7 cells immobilized in -carrageenan, it was necessary to eliminate the fumarase activity which converts fumaric acid to l-malic acid. Several treatments for specifically eliminating fumarase activity from EAPc-7 cells were tested and it was found that when EAPc-7 cells were treated in a culture broth (pH 4.9) containing 50 mM l-aspartic acid at 45° C for 1 h, fumarase activity was almost completely eliminated without inactivation of the aspartase.The treated cells, immobilized in -carrageenan, were used for continuous production of l-aspartic acid from ammonium fumarate. The formation of l-malic acid was negligible and the half-life of the immobilized preparation was 126 days.Productivity of immobilized preparation of treated EAPc-7 cells in l-aspartic acid production was six times of that of the parent cell preparation.     

Transductional construction of a threonine-hyperproducing strain of Serratia marcescens: lack of feedback controls of three aspartokinases and two homoserine dehydrogenases.

To construct a threonine-hyperproducing strain of Serratia marcescens Sr41, the six regulatory mutations for three aspartokinases and two homoserine dehydrogenases were combined in a single strain by three transductional crosses. The constructed strain, T-1026, carried the lysC1 mutation leading to lack of feedback inhibition and repression of aspartokinase III, the thrA1(1) mutation desensitizing aspartokinase I to feedback inhibition, the thrA2(1) mutation releasing feedback inhibition of homoserine dehydrogenase I, the two hnr mutations derepressing aspartokinase I and homoserine dehydrogenase I, and the etr-1 mutation derepressing aspartokinase II and homoserine dehydrogenase II. The strain produced ca. 40 mg of threonine per ml of medium containing sucrose and urea. Furthermore, the productivity of strain T-1026 was compared with those of strains devoid of more than one of the six regulatory mutations.     

Continuous production of glutathione by immobilized Saccharomyces cerevisiae cells

Summary Glutathione was continuously produced by an immobilized Saccharomyces cerevisiae IFO 2044 cell column. The production of glutathione was strongly influenced by the level of activity of the glycolytic pathway. This activity was maintained constant by the addition of NAD.Abbreviations ADP adenosine-5-diphosphate - ATP adenosine-5-triphosphate - NAD nicothinamide adenine dinucleotide     

Threonine production by regulatory mutants of Serratia marcescens.

beta-Hydroxynorvaline (alpha-amino-beta-hydroxyvaleric acid)-resistant mutants of Serratia marcescens deficient in both threonine dehydrogenase and threonine deaminase were isolated and characterized. One of the mutants, strain HNr21, lacked feedback inhibition of threonine-sensitive aspartokinase and homoserine dehydrogenase, was repressed for the two enzymes, and produced 11 mg of threonine per ml of medium containing a limiting amount of isoleucine. The other mutant, strain HNr59, was constitutively derepressed for aspartokinase and homoserine dehydrogenase. Its kinase was sensitive to feedback inhibition, but its dehydrogenase was insensitive to feedback inhibition. This strain produced 5 mg of threonine per ml of medium containing either a limiting or an excess amount of isoleucine. Diaminopimelate auxotrophs derived from strain HNr59 produced more threonine (13 mg/ml) than the parent strain. However, similar auxotrophs derived from strain HNr21 produced the same amount of threonine as that produced by the parent strain.     

Threonine degradation by Serratia marcescens.

The wild strain of Serratia marcescens rapidly degraded threonine and formed aminoacetone in a medium containing glucose and urea. Extracts of this strain showed high threonine dehydrogenase and "biosynthetic" threonine deaminase activities, but no threonine aldolase activity. Threonine dehydrogenase-deficient strain Mu-910 was selected among mutants unable to grow on threonine as the carbon source. This strain did not form aminoacetone from threonine, but it slowly degraded threonine. Strain D-60, deficient in both threonine dehydrogenase and threonine deaminase, was derived from strain Mu-910 and barely degraded threonine. A glycine-requiring strain derived from the wild strain grew in minimal medium containing threonine as the glycine source, whereas a glycine-requiring strain derived from strain Mu-910 did not grow. This indicates that threonine dehydrogenase participates in glycine formation from threonine (via alpha-amino-beta-ketobutyrate) as well as in threonine degradation to aminoacetone.     

Construction of an L-arginine-producing mutant in Serratia marcescens. Use of the wide substrate specificity of acetylornithinase.

L-Arginine biosynthesis in Serratia marcescens Sr41 was found to be controlled by (a) feedback inhibition of N-acetylglutamate synthetase and (b) repression of some L-arginine biosynthetic enzymes, and an L-arginine-degrading system was found to exist. Accordingly, an L-arginine-producing mutant (aru argR argA) of S. marcescens Sr41 was constructed as follows. A mutant incapable of L-arginine utilization (aru) was obtained from the wild strain. Subsequently, from the lysine auxotroph (lysA) of aru mutant, a mutant having derepressed L-arginine biosynthetic enzymes (argR) was isolated by screening for colonies that could utilize Nalpha-acetyl-L-lysine in the presence of L-arginine. This selection was based on the finding that acetylornithinase of S. marcescens hydrolyzed Nalpha-acetyl-L-lysine. On the other hand, to obtain a mutant with feedback-resistant N-acetylglutamate synthetase (argA), the proAB argD argR triple mutant was isolated from the indirectly suppressed revertant (proAB argD) of the proline auxotroph (proAB). Next, the argA mutant was isolated from the triple mutant by selection for resistance to 3,4-dehydro-DL-proline in the presence of L-arginine. The argA mutation was introduced into the aru lysA argR strain by PS20-mediated cotransduction with lysA+. The aru argR argA lysA+ transductant produced 25 mg/ml of L-arginine in the medium.     

Conversion of Glycerol to Dihydroxyacetone by Immobilized Whole Cells of Acetobacter xylinum

Enzymatic production of dihydroxyacetone (DHA) was studied by immobilization of the whole cells of acetic acid bacteria capable of oxidizing glycerol to DHA. Acetobacter xylinum A-9 cells immobilized in a polyacrylamide gel were selected as the most favorable enzyme preparation. The enzymatic properties of immobilized cells converting glycerol to DHA were investigated and compared with those of intact cells. The optimum pH for the immobilized cells was broad (4.0 to 5.5), whereas the intact cells had a narrow pH optimum at 5.5. The thermal stability of the immobilized cells was somewhat higher than that of the intact cells. Apparent K_m values for glycerol with both intact and immobilized cells were about equal, 6.3 × 10⁻² to 6.5 × 10⁻² M. The complete conversion of glycerol to DHA was achieved within 40 h under optimum conditions, and pure crystalline DHA was readily isolated from the reaction mixture with over 80% yield.