Xylan structure,microbial xylanases,and their mode of action

Xylans, the major portion of the hemicellulose of plant cell walls and grasses, are heteropolymers consisting principally of xylose and arabinose. Microbial xylanases with different multiplicities and properties are reported. Most studies on the mode of action of these xylanases have been carried out with fungi and there is very little information available on bacterial xylanases. Fungal xylanases have three or more substrate binding sites: for exampleAspergillus niger, Ceratocytis paradoxa, Cryptococcus albidus andChainia sp. endoxylanases have four to seven subsites with the catalytic site located at the centre of these sub-sites. The analysis of these sub-sites is either by kinetic or end-product analysis studies. Kinetic studies are used for exo-type enzymes while the end-product analysis studies are more convenient for endo-type enzymes. This review covers microbial xylanases with special emphasis on studies of sub-site mapping. The industrial applications of the microbial xylanases are also discussed.     

Management of Root-knot Nematodes by Phenamiphos Applied through an Irrigation Simulator with Various Amounts of Water

Phenamiphos (6.7 kg a.i./ha) was applied via an irrigation simulator to squash at planting (AP) and 2 weeks after planting (PP), and to corn AP and 1 week PP to manage root-knot nematodes (Meloidogyne incognita). The nematicide was applied with 0.25, 0.64, 1.27, and 1.91 cm surface water/ ha to a Lakeland sand in which the soil moisture was at or near field capacity. Based on efficacy and crop response, no additional benefits resulted when phenamiphos was applied in volumes of water greater than 0.25 crn/ha. The cost of applying each 0.25 cm of water over a hectare is approximately $1.08, or a 92% reduction in nematicide application cost over conventional methods ($13.50/ha). Low root-gall indices and high yields from squash and corn indicate more effective nematode management when phenamiphos was applied AP rather than PP. Results from this method of applying phenamiphos suggest that certain nematicides could be used as salvage alternatives when nematodes are detected in crops soon after planting. For multiple-pest management, nematicides, other compatible biocides, and fertilizers could be applied simultaneously with sprinkler irrigation.     

The isolation and characterization of ngm2, a mutation that affects nitrosoguanidine mutagenesis in yeast

Summary We have isolated and characterized a new mutant of Saccharomyces cerevisiae, carrying a single mutant allele that we designate ngm2-1, which is defective with respect to induced mutagenesis. This mutant was isolated by screening mutagenized clones for reduced frequencies of reversion of the his1-7 allele, induced by N-methyl-N-nitro-N-nitrosoguanidine. As judged by the reversion of his1-7 and ilv1-92, ngm2-1 mutant strains are also deficient with respect to mutability induced by methyl methane sulfonate, ethyl methane sulfonate and, at least partially, by UV. UV-induced reversion of the ochre mutation arg4-17 and the frameshift mutation his4-38 was not much affected by ngm2-1, however. Like rev3 and rev7 mutations, ngm2-1 also has little influence on the reversion of the proline missense allele, cyc1-115. Ngm2-1 mutants are only at best very slightly more sensitive to the toxicity of the four mutagens used, and homozygous diploids sporulate normally.     

应用X光荧光法检测硫的化学位移和研究病毒感染植物中硫状态的改变

应用双晶X光荧光光谱仪研究生理性和病理性植物组织中某些元素的分布特征已有报道。本研究工作中采用日本国东芝厂出品的AFV701型双晶X光荧光光谱仪,测定并比较了植物感染病毒前、后的叶片中,不同硫状态相对比例的改变。应用此仪器首先测定各种标准硫化物硫状态的化学位移数值,在确定标准图谱及可分性之后,再测定感染蚕豆萎蔫病毒(BBWV)、黄瓜花叶病毒(CMV)、芜菁花叶病毒(TuMV)的茄、苋色藜、烟草和萝卜等四种寄主植物的显症病叶中不同硫状态的相对比例。发现应用此技术能明显地区别出病态植物与健康植物中硫状态相对比例的变化差异。     

Radiation chemistry of a multicomponent aqueous system relevant to chemistry of cometary nuclei

Summary We have examined a water-dominated multicomponent system after irradiation in the multimegarad dose range with gamma rays from a⁶⁰Co source at both 77 and 310 K. The constituents were simple organic compounds in the proportions in which they appear in a dense interstellar cloud: HCN/CH₃OH/CH₃CN/C₂H₅CN/HCOOH=10.60.20.10.05. The total amounts were adjusted to correspond to a carbon to nitrogen ratio of 1.8 and a water content of about 50% in a cometary nucleus where the dust to volatiles ratio is 1; the total amount of CN-bearing compounds was taken to correspond to 0.4% of the cometary mass. In experiments at 310 K about 40 radiolytic products are identified, among them aldehydes and amino and carboxylic acids. Abundant polymeric material (M_w up to 80,000 daltons) is formed. The basic aspects of radiolysis of the liquid system are present also at 77 K, although at radiation-chemical yields that are lower by one to two orders of magnitude. We have considered the relevance of the present findings to the chemistry of a liquid-water core and the icy layers of a cometary nucleus.     

Radiation chemistry of an aqueous solution of glycine: compounds of interest to chemical evolution studies

Summary We have examined the radiolysis of an O₂-free aqueous solution of glycine at absorbed doses of⁶⁰Co gamma-radiation of up to 20 Mrad. At least 20 compounds are formed during radiolysis, among them several amino acids, an oligoamine, and the nitrogen-free polymers (M_w28,000 daltons). When dicyandiamide is present in the solution of glycine, various nitrogen-containing products, including some polymers (M_w12,000 daltons), are synthesized along with radiolytic products of glycine; polyglycines are not formed. We have determined the radiation-chemical yields of radiolytic-product formation and of decomposition of glycine, and have considered possible free-radical reactions leading to the radiation-induced changes observed.     

Chemical composition of whole plant and grain and yield of nutrients in grain of five barley cultivars

Summary twenty seven field experiments were conducted to determine if there were differences between five barley cultivars in their ability to utilize soil nutrients. There were significant differences among cultivars in yield of grain and in concentration of all macro and micro nutrients examined in both the whole plant and grain.Gateway ranked the highest for the concentration of Na, Mn, and Cu in the whole plant and was among the cultivars with highest concentration of Ca, Fe, and Zn. Centennial had generally the lowest concentration of all the nutrients determined in the whole plant. For the concentrations of Na, Mg, and Cu in grain Gateway ranked highest, but ranked third for the concentrations of K, Ca, Fe, Mn, and Zn in grain. Galt had the highest K and Mg concentration and lowest Mn, Cu and Zn concentration in grain. Except for K concentration in grain, Centennial had the lowest concentrations of all other cationic nutrients in grain.Yield of grain rather than nutrient concentration was the most important criteria in determining the ranking of nutrient yields per hectare. Because of its high grain yield, Bonanza produced the largest yield of micronutrient cations and was second to Galt in production of macronutrient cations, although it was lowest in macronutrient cation concentration. Similarly, Bonanza and Galt had the lowest protein concentration, but produced the highest yield of protein per hectare.The implications for animal nutrition of different levels of nutrients between cultivars are discussed.     

Cleavage of Rabbit Myelin Basic Protein by Plasmin: Isolation and Identification of the Major Products

Rabbit myelin basic protein (BP) was subjected to partial cleavage with plasmin, and 15 cleavage products were isolated by a combination of gel filtration and ion-exchange chromatography. Their identification was achieved by amino acid analysis and tryptic peptide mapping, supplemented in some instances by carboxy-terminal analyses with carboxypeptidases A, B, and Y and amino-terminal analyses with dipeptidyl aminopeptidase I. The results showed that major plasmic cleavage sites included the Lys89-Asn90, Lys133-Ser134, and Lys153-Leu154 bonds. Cleavages also occurred at the Arg31-His32, Lys53-Arg54, and Arg25-His26 bonds, but these appeared to be less extensive. A large number of additional peptides were produced in relatively low yield. The smaller of these were isolated from heterogeneous fractions by high-voltage electrophoresis-TLC. Amino acid analysis of these peptides showed that minor cleavage sites included the Arg9-His10, Lys13-Tyr14, Lys103-Gly104, Lys137-Gly138, Lys140-Gly141, and Arg160-Ser161 bonds. In spite of a lower selectivity toward peptide bonds in BP as compared with pepsin, cathepsin D, and thrombin, plasmin has the advantage over the former proteinases in that it does not cleave at or near the Phe44-Phe45 bond. Instead it cleaves at the Arg31-His32 and Lys53-Arg54 bonds, thus preserving the entire hydrophobic sequence Ile-Leu-Asp-Ser-Ile-Gly-Arg-Phe-Phe as well as short sequences to either side.     

Effect of 6-hydroxydopamine on neuropeptides in the rat female genitourinary tract

The occurrence and distribution of neuropeptide Y has been determined in the rat female genitourinary tract by radioimmunoassay and chromatographic analysis. Within the bladder, higher concentrations of neuropeptide Y were found in the trigone (48.8±5.2 pmol/g) than in the dome (36.0±2.1 pmol/g). In the genital tract, highest concentrations were identified in the vagina (41.4±2.1 pmol/g). Treatment of rats with 6-hydroxydopamine resulted in significant depletion of neuropeptide Y concentrations in both parts of the bladder, together with vagina, uterine horn and fallopian tube. No change was observed in the cervix, uterine body and ovary. Concentrations of vasoactive intestinal polypeptide were unaffected by treatment with 6-hydroxydopamine except in the area of the cervix where concentrations rose from 64.1±5.7 pmol/g to 133.6±15.1 pmol/g (p<0.05). There was a generalised, but statistically insignificant rise in substance P concentrations.