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The degradation of N-lauroyl-l-valine in soil and the effects of sunlight and ultraviolet radiation on this compound were studied. When N-lauroyl-l-valine was added to the soil extract, a precipitate was observed. The precipitate was thought to be a salt formed from one calcium atom and two molecules of N-lauroyl-l-valine. These data indicated that N-lauroyl-l-valine was absorbed firmly in the soil. Qualitative analysis of compounds formed during incubation of soil with N-lauroyl-l-valine was investigated by gas chromatography. Laurie acid (C12) and capric acid (C10) were detected in the medium after incubation. The amino acid could be determined quantitatively by a microbial assay method. The experiment using N-lauroyl-l-valine (14C) indicated that 14CO2 was produced as a final product. These data suggested that N-lauroyl-l-valine was spilt to lauric acid and l-valine, and the lauric acid was degraded to CO2 through capric acid by β-oxidation. The parent compound, N-lauroyl-l-valine was stable to sunligh...

As a part of studies on the mechanism of action of antibiotics polyoxins, effects of various N-aminoacyl derivatives of polyoxin C and other polyoxins on chitin-UDP acetylglucosaminyl-transferase (EC 2.4.1.16, chitin synthetase) prepared from phytopathogenic fungus Piricularia oryzae were investigated. It was found that they inhibited the enzyme in competition with the substrate UDP-N-acetylglucosamine, Inhibitor constants, Ki, for these polyoxins were determined and the values of binding affinity, −ΔGbind of the inhibitors to the enzyme were calculated from the Ki values. In addition, by using these −ΔGbind values the values of partial binding affinity, −Δg for the several atoms and atomic groups or the several moieties contained in the polyoxin J molecule were estimated. From the results obtained, it was concluded that the carbamoylpolyoxamic acid moiety of polyoxins helps to stabilize the polyoxin-enzyme complex through the contributions of its oxygen atom at C−1″, amino group at C−2″, hydroxyl groups at C−3″ and C−4″, aliphatic carbon chain and terminal carbamoyloxy group. The results obtained by the kinetic investigation using various nucleotides and nucleotide sugars suggested that there was a specific binding site on the enzyme corresponding to the uridine moiety of UDP-N-acetylglucosamine, and that the pyrimidine nucleoside moiety of polyoxins was also bound to this site.

Various derivatives of polyoxin C, other polyoxins and several uridine analogues have been known as competitive inhibitors of chitin-UDP acetylglucosaminyitransferase (EC 2.4.1.16, chitin synthetase). Their inhibitory activities were more or less dependent on pH. The variation of inhibitor constants Ki or Michaelis-Menten parameters Km and V with pH was investigated and the data obtained were plotted according to the method proposed by Dixon et al. From the results of the pKi-pH plots for the above competitive inhibitors, it was concluded that the ionized amino group at C−2″ position acted a very important role for the binding of polyoxins to chitin synthetase. The carbonyl oxygen atoms at C−1″ and of the carbamoyloxy group probably participated in the hydrogen bond formation with the enzyme. And pH scarcely influenced on the interaction between the carboxyl group at C−5″ and the enzyme. The results of the Dixon plots for variations of Km and V with pH suggested that an unionized imidazole group (pKa = 6.3) and an ionized amino group (pKa = 7.7) of chitin synthetase were concerned in the enzyme reaction.

Blasticidin S deaminase (EC 3.5.4.23) was purified by affinity chromatography using a column of Sepharose 4B coupled with pyrimidinoblasticidin S as a ligand. The Michaelis constant Km and the maximum velocity Vmax varied with pH, which suggests that enzyme ionization is important either for substrate binding or for catalytic activity. The inflection point at pH 8.6-8.9 in the plot of pKm versus pH was attributed to an enzyme amino group which corresponded to the carboxyl group of substrates, and an inflection at pH 5.3 in the log Vmax-pH plot was assigned to the imidazole group of histidine, which appeared to be critical for catalytic deaminohydroxylation. The binding of substrates by the enzyme was inferred to be promoted thermodynamically, and activation of the substrate-enzyme complex was presumed to proceed endothermically. From the results obtained, a hypothetical mode of reaction for blasticidin S deaminase is proposed.

(1) Chitin-UDP acetylglucosaminyltransferase (E.C. 2.4.1.16., chitin synthetase) in the cell-free system from phytopathogenic fungus Piricularia oryzae, and effects of various polyoxins and related compounds on the enzyme activity were studied. Polyoxins A~M, polyoxin A derivatives, polyoxin C derivatives, 5′-amino-5′-deoxyuridine, uridine and thymidine inhibited equally the incorporation of N-acetylglucosamine (GlcNAc) from UDP-N-acetylglucosamine (UDP-GlcNAc) into chitin.(2) Competition between the above inhibitors and UDP-GlcNAc was observed by kinetic studies. The Km for UDP-GlcNAc was determined to be 3.3 × 10−3 m and the Ki values for polyoxins A~M, except polyoxin C, were found to be in the range of 3.3 × 10−5 m to 3.4 × 10−6 m. For polyoxin C, 5′-amino-5′-deoxyuridine and uridine, the Ki values of 2.7 × 10−3 m, 8.0 × 10−3 m and 3.0 × 10−3 m were given, respectively. The inhibitor constants for other related compounds were also calculated.(3) The values of binding affinity, −ΔG, for formation of su...

In the previous papers we reported that the antibiotic Polyoxin D induced the characteristic swelling of the mycelia of fungi,1,2) and strongly inhibited the incorporation of 14C-glucosamine into the fungal cell wall chitin.3) The present work has been conducted to further investigate the influence of this antibiotic on the fungal cell wall biosynthesis.Polyoxin D did not inhibit the incorporation of 14C-glucose, 14C-amino acids and 14C-sodium acetate into the cell wall. In addition, UDP-N-acetylglucosamine, a precurcor of chitin biosynthesis of cell wall, was accumulated in the Polyoxin D-treated mycelia of Cochliobolus miyabeanus more than 150 to 160% of that accumulated in the untreated one.Chitin synthetase prepared from Piricularia oryzae which is not treated with Polyoxin D was completely inhibited by the addition of 0.1 ppm of Polyoxin D. The fungitoxicity of Polyoxins A to G was positively related to their inhibition of 14C-glucosamine incorporation into the cell wall chitin of C. miyabeanus. From...

In the previous papers we reported that the antibiotic Polyoxin D induced the characteristic swelling of the mycelia of fungi,1,2) and strongly inhibited the incorporation of 14C-glucosamine into the fungal cell wall chitin.3) The present work has been conducted to further investigate the influence of this antibiotic on the fungal cell wall biosynthesis.Polyoxin D did not inhibit the incorporation of 14C-glucose, 14C-amino acids and 14C-sodium acetate into the cell wall. In addition, UDP-N-acetylglucosamine, a precurcor of chitin biosynthesis of cell wall, was accumulated in the Polyoxin D-treated mycelia of Cochliobolus miyabeanus more than 150 to 160% of that accumulated in the untreated one.Chitin synthetase prepared from Piricularia oryzae which is not treated with Polyoxin D was completely inhibited by the addition of 0.1 ppm of Polyoxin D. The fungitoxicity of Polyoxins A to G was positively related to their inhibition of 14C-glucosamine incorporation into the cell wall chitin of C. miyabeanus. From...

(1) Chitin-UDP acetylglucosaminyltransferase (E.C. 2.4.1.16., chitin synthetase) in the cell-free system from phytopathogenic fungus Piricularia oryzae, and effects of various polyoxins and related compounds on the enzyme activity were studied. Polyoxins A~M, polyoxin A derivatives, polyoxin C derivatives, 5′-amino-5′-deoxyuridine, uridine and thymidine inhibited equally the incorporation of N-acetylglucosamine (GlcNAc) from UDP-N-acetylglucosamine (UDP-GlcNAc) into chitin.(2) Competition between the above inhibitors and UDP-GlcNAc was observed by kinetic studies. The Km for UDP-GlcNAc was determined to be 3.3 × 10−3 m and the Ki values for polyoxins A~M, except polyoxin C, were found to be in the range of 3.3 × 10−5 m to 3.4 × 10−6 m. For polyoxin C, 5′-amino-5′-deoxyuridine and uridine, the Ki values of 2.7 × 10−3 m, 8.0 × 10−3 m and 3.0 × 10−3 m were given, respectively. The inhibitor constants for other related compounds were also calculated.(3) The values of binding affinity, −ΔG, for formation of su...

Studies were conducted on the influence of Kitazin analogues on the incorporation of 14C-glucosamine into the mycelial cell wall fraction of Pyricularia oryzae. Compounds of thiolates and phosphates, both having in vitro inhibitory activities toward the mycelial growth, inhibited the incorporation, whereas those of thionates and dithioates, either having no fungitoxicity, did not inhibit the incorporation. Mycelia of P. oryzae treated with Kitazin-P (S-benzyl O,O′-diisopropyl phosphrothioate; IBP) accumulated about twice as much an amino sugar derivative as untreated ones. Mycelia treated with thiono or dithio analogues, which have no fungitoxicity, showed no accumulation. The accumulated substance gave a identical spot with authentic UDP-N-acetyl glucosamine on paper chromatograms developed with four solvent systems.

(1986). New Antibiotics, Albopeptins A and B. Agricultural and Biological Chemistry: Vol. 50, No. 8, pp. 2163-2165.