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Biomedical subjects

I Chibata

Publications and source records attributed to I Chibata.

At least 73 records · Page 4Linked to original sources
PubMed1976

Biosynthesis of norvaline, norleucine, and homoisoleucine in Serratia marcescens.

The biosynthetic pathways of norvaline homoisoleucine were examined using regulatory mutants of leucine biosynthesis in Serratia marcescens. alpha-Isopropylmalate synthetase [EC 4.1.3.12], the first enzyme of leucine biosynthesis, catalyzed the condensations of acetyl-CoA with pyruvate, alpha-ketobutyrate, alpha-ketovalerate, or alpha-keto-beta-methylvalerate as well as alpha-ketoisovalerate. These condensations were inhibited by leucine in the alpha-aminobutyrate-resistant mutant, a mutant with derepressed leucine biosynthetic enzymes. However, these condensations were coordinately desensitized in the isoleucine leaky revertant, a leucine accumulator. The formation of norvaline or homoisoleucine was greater in the leucine accumulator, but its leucine auxotroph did not form these unnatural amino acids. Thus, norvaline and homoisoleucine are considered to be formed from alpha-ketobutyrate and alpha-keto-beta-methylvalerate by the leucine biosynthetic enzymes. This view was confirmed by the findings that a norvaline accumulator could be obtained by derivation of the leucine accumulator into an isoleucine-valine auxotroph. Norleucine was also found to be formed from alpha-ketovalerate, an alpha-ketoacid corresponding to norvaline.

2-Isopropylmalate Synthase↗
PubMed1976

Mechanism of D-alanine production by Corynebacterium fascians.

The amounts of extracellular D-alanine accumulated by Corynebacterium fascians ATCC 21950 in a medium containing glycerol as the sole carbon source is increased to almost 12 mg/ml by adding pyruvate to the medium. Cell-free extracts of C. fascians were shown to possess both L-alanine dehydrogenase and alanine racemase activities. These results indicated that a mechanism exists that allows this microorganism to synthesize D-alanine from pyruvate. A study comparing the optical purity of the intracellular alanine and the extracellular alanine suggested that the cell membrane possesses the stereospecific permeability for D-alanine. Thus, it may be concluded that L-alanine is first formed from pyruvate by L-alanine dehydrogenase and then converted to D-alanine by racemase inside the cells. Subsequently, only D-alanine leaks out stereospecifically through the cell membrane, and large amounts of D-alanine accumulate in the extracellular medium.

Alanine↗
PubMed1976

Nitrogen source primarily supplied by amino acids and the efficacy for maximal growth of rats.

The effect of osmotic pressure of diets on be food intake of young rats was investigated by comparing the nutritional effect of casein with the corresponding amino acid mixture at 3.2% nitrogen level. Changes in the osmolarity of diets due to the type of dietary carbohydrate had a little effect on food intake, whereas partial substitution of casein for amino acids resulted in significant increase in food intake. Weight gain and food intake of rats fed the 25% replaced amino acid diet were compared with those of rats fed the casein diet. Food intake was lower at 12.5% replacement than at 25% replacement. These observation suggest that a well-balanced amino acid mixture supported maximal growth of rats when 25% of the amino acid mixture was replace with casein. This suggestion could be experimentally confirmed by using an amino acid mixture based on the amino acid composition of whole-egg protein.

Amino Acids↗
PubMed1975

Crystallographic studies on L-asparaginase from Proteus vulgaris. II. Symmetry and location of the tetrameric molecule.

Analyses of the x-ray diffraction intensity data by the Patterson synthesis and rotation function techniques show that the true space group of the monoclinic crystals of L-asparaginase (L-asparagine amidohydrolase, EC 3.5.1.1) from Proteus vulgaris is P21, that the molecular centers lie at x = 0.054, y = 0, z = 0.256, and its symmetry related positions, and that the tetramer molecules possess three approximate, mutually perpendicular 2-fold rotational symmetries, the axes of which run along the directions of the crystallographic a*-, b-, and c-axes. In addition, an investigation of the molecular packing arrangement in the crystal indicates that the tetramer molecules possess an approximately regular tetrahedral subunit structure.

Asparaginase↗
PubMed1975

Crystallization and properties of L-arginine deiminase of Pseudomonas putida.

Crystalline L-arginine deiminase of Pseudomonas putida was prepared by the following steps: sonic disruption, ammonium sulfate fractionation, protamine sulfate treatment, DEAE-cellulose column chromatography, and L-arginine-Sepharose 6B chromatography followed by crystallization. This procedure yields a crystalline pure enzyme with a 45% recovery of the activity in crude cell-free extracts. The yield is significantly higher than that reported for this enzyme. The purified enzyme appears to be homogeneous in ultracentrifugation (s-o20, w equals 10.2 S) and isoelectric focusing (pI equals 6.13). The purified enzyme showed two bands on disc gel electrophoresis, both carrying out the deimination of L-arginine. Electrophoresis in the presence of beta-mercaptoethanol plus Na dodecyl-SO4 gave a single band (Mr, 54,000). Specific activity of this enzyme was 58.8 mumol of L-citrulline formed per min per mg of protein at 37 degrees. The optimum pH of the purified enzyme was 6.0 and maximal activity was obtained at 50 degrees. The molecular weight of the native protein was 130,000 by gel filtration and 120,000 by sedimentation-equilibrium measurements. The spectrum of the pure enzyme showed absorption maximum at 280 nm and the value of E-1%-1 CM AT 280 NM WAS 10.48 IN 0.05 M potassium phosphate buffer (pH 7.0). The crystalline enzyme hydrolyzed several L-arginine analogues. L-Homoarginine, L-alpha-amino-gamma-guanidinobutyric acid, and L-alpha-amino-beta-guanidinopropionic acid competitively inhibited the hydrolysis of L-arginine with Ki values of 25.7, 7.5, and 4.0 times 10- minus 3 M, respectively. p-Chloromercuribenzoate, Ag-+, and Hg-2+, and several metal ions inhibited the enzyme.

Arginine↗
PubMed1975

Crystalline L-histidine ammonia-lyase of Achromobacter liquidum. Crystallization and enzymic properties.

Crystalline L-histidine ammonia-lyase of Achromobacter liquidum was prepared with a 24% recovery of the activity. The specific activity of the pure enzyme (63 mumol of urocanic acid min-1 mg-1) is similar to those so far reported for the enzyme from other sources. The purified enzyme appeared to be homogeneous by analytical disc electrophoresis and isoelectric focusing (pI = 4.95). The molecular weight determined by Sephadex G-200 gel filtration is 200000. The optimum pH is 8.2, and the optimum temperature is 50 degrees C. The enzyme showed strict specificity to L-histidine (Km = 3.6 mM). Several histidine derivatives are not susceptible to the enzyme but do inhibit the enzyme activity competitively; the most effective inhibitors are L-histidine methyl ester (Ki = 3.66 mM) and beta-imidazole lactic acid (Ki = 3.84 mM). L-Histidine hydrazide (Ki = 36 mM) and imidazole (Ki = 6 mM) noncompetitively inhibited the enzyme EDTA markedly inhibited enzyme activity and this inhibition were reversed by divalent metal ions such as Mn2+, Co2+ Zn2+, Ni2+, Mg2+, and Ca2+. These results suggest that the presence of divalent metal ions is necessary for the catalytic activity of histidine ammonia-lyase. Sodium borohydride and hydrogen peroxide inhibited the enzyme activity.

Alcaligenes↗
PubMed1975

Engineering analysis of continuous production of L-aspartic acid by immobilized Escherichia coli cells in fixed beds.

The reaction mechanism and decay behavior of aspartase activity for immobilized Escherichia coli cells were investigated by using a sectional packed column. Reaction within the immobilized cell column proceeded at zero-order on substrate solutions ranging in concentration from 0.1 to 1.0M, and the initial reaction rate was found to be 1.556 X 10(-2) mol/min/liter of immobilized cells. The effect of temperature on the reaction rate constant was investigated. The Arrhenius plot was a straight line at temperatures below 43 degrees C, and the activation energy for immobilized cells was calculated to be 12.36 kcal/mol. Aspartase activity in the immobilized cell column decayed exponentially and uniformly in all sections of a column. Its half-life was approximately 120 days. The rate of formation of L-aspartic acid was shown to be independent of column dimensions.

Aspartate Ammonia-Lyase↗
PubMed1975

Effects of pyridoxal phosphate N-oxide and 2'-hydroxy pyridoxal phosphate on L-aspartate beta-decarboxylase.

Pyridoxal phosphate N-oxide and 2'-hydroxypyridoxal phosphate served as the coenzyme for aspartate beta-decarboxylase (EC 4.1.1.12) from Pseudomonas dacunhae. Reconstituted enzymes with those pyridoxal phosphate analogues exhibited an absorption band near 370 nm. Close to 1 mole of vitamin B6 derivative is bound per minimal catalytic unit with high affinity. The decarboxylase, desulfinase, and transaminase activites of the both pyridoxal phosphate derivate-enzymes are relatively low. But the Km values for aspartate and cysteine sulfinate are not affected.

Aspartic Acid↗
PubMed1974

Production of flavine-adenine dinucleotide from riboflavine by a mutant of Sarcina lutea.

A study was made to develop a new method for the production of flavine-adenine dinucleotide (FAD) from riboflavine and adenine by a mutant of Sarcina lutea deficient in the enzyme adenosine deaminase. It was found that this strain could convert exogenously supplemented riboflavine to extracellular FAD. The yields of FAD were increased by addition of D-cycloserine in the culture medium. The culture conditions for FAD production were investigated under the addition of D-cycloserine, and increased production of FAD was observed with the addition of an appropriate amount of thiamine, acetate, and sodium ion. The yield of 0.7 g/liter was obtained in the optimal culture in 5 days. Accumulated FAD was readily isolated by adsorption chromatography and ion-exchange chromatography in a 70% yield.

Acetates↗