Flower-Inducing Activity of Exogenous Lysine in Lemna paucicostata 151 Cultured on Nitrogen-Rich Medium

Flower-inducing activity of lysine was examined in Lemna paucicostata151, a weakly responsive short-day plant, cultured on nitrogen-richmedium under long-day conditions (continuous light). Lemna paucicostata151 was homogenized in a solution of lysine and the homogenatewas centrifuged. The supernatant (lysine-containing extract)was added to nitrogen-rich medium after passage through a membranefilter to give various concentrations of lysine in the medium.Flowering was induced in plants grown for six days on mediumthat contained lysine at concentrations above 0.25 µM.In plants grown on medium that contained 1 µM lysine,a significant flowering response was observed on the fourthday of culture. However, the flower-inducing activity of lysinedisappeared when the lysine-containing extract was added tothe medium and the medium was then autoclaved, suggesting thatthe active principle is unstable to autoclaving. Among derivativesof lysine tested, lysine hydroxamate had the highest flower-inducingactivity and lysyl lysine had almost same activity as that oflysine. When added to the medium without homogenization withplant material, lysine and lysyl lysine had flower-inducingactivity but lysine hydroxamate did not induce flowering. (Received April 26, 1993; Accepted November 8, 1993)     

D-malic acid production from DL-malic acid by enantiospecific assimilation with Acinetobacter lwofii

Summary Acinetobacter lwofii ATCC 9036 assimilated L-malic acid eantiospecifically and left D-malic acid when grown in a medium containing DL-malic acid. The optical purity of the D-malic acid isolated from the culture filtrate was 100%. When the organism was incubated at 26°C, 220 r.p.m. in a Erlenmeyer flask containing 100g/l of disodium maleate, L-malic acid was completely consumed during 7 days incubation and D-malic acid remained at the concentration of 35g/l.     

Purification and characterization of pig lung carbonyl reductase.

A pyrazole-sensitive carbonyl reductase from pig lung was purified to homogeneity by electrophoretic criteria. Chemical cross-linking study suggested that the native enzyme is a tetramer with a Mr of 103,000, consisting of apparent identical subunits of Mr 24,000. The enzyme reduced aliphatic and aromatic carbonyl compounds with NADPH as a preferable cofactor to NADH and catalyzed the oxidation of secondary alcohols and the aldehyde dismutation in the presence of NAD(P)+. Immunohistochemical study with the antibodies against the enzyme revealed that the enzyme was localized in the ciliated cells, nonciliated bronchiolar cells, Type II alveolar pneumocytes, and the epithelial cells of the ducts of the bronchial glands in the pig lung. In addition to the properties and distribution, the pig lung enzyme was immunochemically similar to the pulmonary enzymes in the guinea pig and mouse. However, the pig enzyme showed the following unusual features. (1) The enzyme exhibited an equatorial specificity in the reduction of 3-ketosteroids; the 4-pro-S hydrogen of NADPH was transferred to the carbonyl carbon atom of 5 alpha- and 5 beta-androstanes, and the respective reduced products were identified as 3 beta- and 3 alpha-hydroxysteroids. (2) Although the NADPH-linked reduction of carbonyl compounds apparently obeyed the Michaelis-Menten kinetics at pH 6.0, the double-reciprocal plots of the velocity vs concentrations of the carbonyl substrates were convex at pH higher than 6.5. The Hill coefficients and [S]0.5 values for the substrates decreased as the pH for reaction increased. The results suggest that the pig enzyme exhibits negative cooperativity with respect to the carbonyl substrates and that the hydrogen ion acts as an allosteric effector abolishing the negative interaction.     

A Novel Isourazole Herbicide, Fluthiacet-Methyl, is a Potent Inhibitor of Protoporphyrinogen Oxidase after Isomerization by Glutathione S-Transferase

A novel isourazole herbicide, fluthiacet-methyl (methyl [[2-chloro-4-fluoro-5-[(5,6,7,8-tetrahydro-3-oxo-lH,3H-[l,3,4]thiadiazolo[3,4-a]pyridazin-l-ylidene)amino]phenyrjthio]acetate;experimental code name, KIH-9201) promoted the leakage of electrolytesfrom cotyledons of velvetleaf (Abtilon theophtasti Medic) andcotton (Gossypium hirsutum L.) plants that are sensitive tothis compound. It induced the accumulation of protoporphyrinIX in cotyledons of cotton and inhibited Chl biosynthesis incotyledons of velvetleaf and cotton at low concentrations (I₅₀values, 10–12 nM). Fluthiacet-methyl was converted toits urazole by glutathione S-transferase that had been partiallypurified from velvetleaf. The urazole inhibited protoporphyrinogenoxidase (Protox, EC 1.3.3.4 [EC] ) from some plants, including velvetleaf,at low concentrations (I₅₀ values, 5.1–11 nM), whereasfluthiacet-methyl was not as potent. The effects in vivo (electrolyteleakage and inhibition of Chi biosynthesis) of fluthiacet-methylwere correlated with the inhibition of Protox activity by theurazole and not with the action of fluthiacet-methyl itself.From these results, it is concluded that fluthiacet-methyl inhibitsProtox activity after conversion to the corresponding urazoleby glutathione S-transferase. It is in this way that fluthiacet-methylexerts its effect as a light-dependent peroxidizing herbicide. (Received November 1, 1994; Accepted March 6, 1995)     

Water Soluble Pigments Containing Xylose and Glucose in Gametangia of the Green Alga, Bryopsis maxima

Several water-soluble pigments were purified from gametangiaof Bryopsis maxima by liquid chromatography and characterizedby pyridylamination and high-performance anion-exchange chromatography.The structure of the main red pigment is proposed based on thedata of infrared spectrum, Mass spectrum, ¹H and ¹³C NMR spectraand pyridylamino analysis. As a consequence, this pigment containeda tetrapyrrole with phytol and a sugar chain comprised of xyloseand glucose. The sequence of the sugars in the chain was determinedbased on its Mass spectrum. The pigment was similar to chlorophyll-originpigments observed in other plants. No aldehyde group, however,was present at C5 in the open tetrapyrrole chain. (Received August 3, 1994; Accepted November 10, 1994)     

Site-directed mutagenesis of histidine residues in Clostridium perfringens alpha-toxin.

Mutagenesis of H-68 or -148 in Clostridium perfringens alpha-toxin resulted in complete loss of hemolytic, phospholipase C, sphingomyelinase, and lethal activities of the toxin. These activities of the variant toxin at H-126 or -136 decreased by approximately 100-fold of the activities of the wild-type toxin. Mutation at H-46, -207, -212, or -241 showed no effect on the biological activities, indicating that these residues are not essential for these activities. The variant toxin at H-11 was not detected in culture supernatant and in cells of the transformant carrying the variant toxin gene. Wild-type toxin and the variant toxin at H-148 bound to erythrocytes in the presence of Ca2+; however, the variant toxins at H-68, -126, and -136 did not. Co2+ and Mn2+ ions stimulated binding of the variant toxin at H-68, -126, and -136 to membranes in the presence of Ca2+ and caused an increase in hemolytic activity. Wild-type toxin and the variant toxins at H-68, -126, and -136 contained two zinc atoms in the molecule. Wild-type toxin inactivated by EDTA contained two zinc atoms. These results suggest that wild-type toxin contains two tightly bound zinc atoms which are not coordinated to H-68, -126, and -136. The variant toxin at H-148 possessed only one zinc atom. Wild-type toxin and the variant toxin at H-148 showed [65Zn]2+ binding, but the variant toxins at H-68, -126, and -136 did not. Furthermore, [65Zn]2+ binding to wild-type toxin was competitively inhibited by unlabeled Zn2+, Co2+, and Mn2+. These results suggest that H-68, -126, and -136 residues bind an exchangeable and labile metal which is important for binding to membranes and that H-148 tightly binds one zinc atom which is essential for the active site of alpha-toxin.     

Enhancement of aromatic amino acid-nucleic acid base stacking interaction by metal coordination to base: fluorescence study on a tryptophan-Pt(II)-guanine ternary complex

In order to investigate the effect of the Pt(II) ion on the stacking interaction between tryptophan and a guanine base, the quenching of Trp fluorescence was monitored for some systems in the absence and presence of the metal ion, and the association constants were obtained by the analysis of Eadie-Hofstee plots. All spectral data suggested that the stacking interaction is enhanced by the Pt(II) coordination to the guanine N7 atom. The result indicates the importance of the metal ion as a bookmark in the specific recognition of a nucleic acid base by an aromatic amino acid residue.     

Numerical simulation of neuronal population coding: influences of noise and tuning width on the coding error

Performance of neuronal population coding is investigated numerically, in neurons with Gaussian tuning functions of various widths and noise ratios. The present model is applicable to both direction coding and orientation coding. It is shown that the coding error exhibits peculiar dependence on the width of the tuning function and that the dependence under the influence of noise is different from that of the noise-free case. In the absence of noise, the coding error increases monotonically with the width of the tuning function. The increment obeys the power law (the exponent estimated is 0.501) when the width is less than the critical value. In this region of the width a scaling law is obtained, which shows that the root-mean-square error is proportional to the square root of the ratio of the width of the tuning function to the population size. When the width exceeds the critical value, the coding error increases more rapidly than the power law. The reason for this anomalous increase, not seen previously, is argued. Existence of noise changes the dependence of the coding error on the width of the tuning function. Unlike the noise-free case, the error under the influence of noise becomes minimum at an intermediate value of the width. The width that gives the minimum coding error is termed the optimum width in this article. The numerical results suggest that the optimum width is roughly proportional to the square root of the noise ratio but has only a weak dependence on the population size. It is further shown that the coding error for the optimum width increases sharply when the noise ratio exceeds about 0.5 and is inversely proportional to the square root of the population size.     

Purification and characterization of two forms of microsomal carbonyl reductase in guinea pig liver.

Glycosaminoglycan oligosaccharides generated by treatment of biosynthetically radiolabelled dermatan sulphate and hyaluronic acid with chondroitin AC lyase or testicular hyaluronidase may be resolved into a series of discrete bands by polyacrylamide-gel electrophoresis. Bands were identified by fixation in glacial acetic acid containing 20% (w/v) 2,5-diphenyloxazole followed by fluorography. The bands represented glycans which differed in size by one disaccharide unit. For the larger oligosaccharides (decasaccharides and above) of similar charge: mass ratio, there was a linear relationship between electrophoretic mobility and log Mr. However, the smaller species showed anomalous migration patterns. Consideration of the structures of the fragments produced by the different enzyme treatments suggests that copolymeric and homopolymeric oligosaccharides may be separated by polyacrylamide-gel electrophoresis. There are many potential applications of this technique, foremost amongst them being studies on the molecular size heterogeneity and patterns of enzyme-mediated depolymerization of native glycosaminoglycan chains and investigations into rates of polymer chain elongation and post-polymerization modification reactions so essential to glycosaminoglycan function.