Purification of a kappa-carrageenase from marine Cytophaga species

A mixture of extracellular carrageenases was isolated from the cell-free medium of a culture of marine Cytophaga sp. 1k-C783 grown on ZoBell 2216 E broth with 0.1% commercial carrageenan. A single active peak of kappa-carrageenase was separated and purified from the mixture by ammonium sulfate precipitation, ion-exchange chromatography, and Sephadex G-200 gel filtration chromatography. Molecular weight of the purified kappa-carrageenase was estimated as 100,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The purified kappa-carrageenase had pH optimum 7.6 and temperature optimum 25 C.     

蚕豆叶片发育与衰老过程中超氧物歧化酶活性与丙二醛含量变化

蚕豆植株叶片随茎节自上而下表现出明显的发育与衰老顺序,可作为衰老特征的是叶绿素和蛋白质含量明显下降。蚕豆叶中SOD活性主要定位于12 000× g离心后所得的上清液和叶绿体组分。衰老叶片的SOD总活性和叶绿体组分的相对活性都有所下降,SOD同工酶谱也发生了改变。O_2~ 产生速率随叶龄增大而稍上升;而MDA含量在叶片外观表现枯黄衰老征兆前就急剧上升。可能因为衰老叶片过氧化氢酶活性大幅度下降与SOD之间的不平衡,致使O_2~ 代谢中间产物累积而引起膜的损伤.     

Influence of high dietary threonine on growth and amino acids in blood and tissues of rats

Summary Diets containing 8 or 15% protein from casein plus limiting amino acids, 25% fat and adequate levels of other nutrients for rat growth were supplemented with 0, 0.5, 1.0, 2.0 or 4% of excess L-threonine. Addition of up to 1% excess threonine had little effect on weight gains or food intakes of weanling rats, but addition of 2 and 4% threonine caused a drastic reduction in weight gains or food intakes (up to 41%); the adverse effect being more severe in rats fed lower protein diets. Addition of graded levels of excess threonine resulted in (5 to 47-fold and 4 to 20-fold) increase in concentration of free threonine in rat plasma and brain, respectively. Addition of excess threonine also caused up to 5-fold increase in plasma level of 3-methylhistidine, suggesting increased muscle protein breakdown.     

Tryptophan-dependent biosynthesis of auxins in soil

The presence of auxins in soil may have an ecological impact affecting plant growth and development. A rapid and simple colorimetric method was used to assess California soils for their potential to produce auxins upon the addition of L-tryptophan (L-TRP). The auxin content measured by colorimetry was expressed as indole-3-acetic acid (IAA)-equivalents. A substrate (L-TRP) concentration of 5.3 g kg^-1, glucose concentration of 6.7 g kg^-1, no nitrogen, pH 7.0, 40°C, shaking (aeration) and 48 h incubation time were selected as standardized conditions to assay for auxin biosynthesis in soil. IAA was confirmed as a major microbial metabolite derived from L-TRP in soil by use of high performance liquid chromatography (HPLC). Under standardized conditions, L-TRP-derived auxins in 19 soils varied greatly ranging from 18.2 to 303.2 mg IAA equivalents (auxins) kg^-1 soil. This study suggests that the phenotypic character of the soil microbiota has more of an influence on auxin production than the soil physicochemical properties (e.g., pH, organic C content, CEC, etc.).     

Biosynthesis of lysosomal hydrolases: their synthesis in bound polysomes and the role of co- and post-translational processing in determining their subcellular distribution

By in vitro translation of mRNA’s isolated from free and membrane-bound polysomes, direct evidence was obtained for the synthesis of two lysosomal hydrolases, β-glucuronidase of the rat preputial gland and cathespin D of mouse spleen, on polysomes bound to rough endoplasmic reticulum (ER) membranes. When the mRNA’s for these two proteins were translated in the presence of microsomal membranes, the in vitro synthesized polypeptides were cotranslationally glycosylated and transferred into the microsomal lumen. Polypeptides synthesized in the absence of microsomal membranes were approximately 2,000 daltons larger than the respective unglycosylated microsomal polypeptides found after short times of labeling in cultured rat liver cells treated with tunicamycin. This strongly suggests that nascent chains of the lysosomal enzymes bear transient amino terminal signals which determine synthesis on bound polysomes and are removed during the cotranslational insertion of the polypeptides into the ER membranes. In the line of cultured rat liver cells used for this work, newly synthesized lysosomal hydrolases showed a dual destination; approximately 60 percent of the microsomal polypeptides detected after short times of labeling were subsequently processed proteolytically to lower molecular weight forms characteristic of the mature enzymes. The remainder was secreted from the cells without further proteolytic processing. As previously observed by other investigations in cultured fibroblasts (A. Gonzalez-Noriega, J.H. Grubbs, V. Talkad, and W.S. Sly, 1980, J Cell Biol. 85: 839-852; A. Hasilik and E.F. Neufeld, 1980, J. Biol. Chem., 255:4937-4945.) the lysosomotropic amine chloroquine prevented the proteolytic maturation of newly synthesized hydrolases and enhanced their section. In addition, unglycosylated hydrolases synthesized in cells treated with tunicamycin were exclusively exported from the cells without undergoing proteolytic processing. These results support the notions that modified sugar residues serve as sorting out signals which address the hydrolases to their lysosomal destination and that final proteolytic cleavage of hydrolase precursors take place within lysosome itself. Structural differences in the carbohydrate chains of intracellular and secreted precursors of cathespin D were detected from their differential sensitivity to digestion with endoglycosidases H and D. These observations suggest that the hydrolases exported into the medium follow the normal secretory route and that some of their oligosaccharides are subject to modifications known to affect many secretory glycoproteins during their passage through the Golgi apparatus.     

The effect of different media and culture techniques on plating efficiency of strawberry mesophyll cells in culture

Mesophyll cells of strawberry were isolated mechanically by a hand homogenizer, One g healthy, fully-expanded leaves yielded 10⁷ cells. The agar culture method was the only culture technique found suitable to obtain any quantitative data.     

Detection of somaclonal variations in tissue cultured date palm (Phoenix dactylifera L.) using transposable element-based markers

Plant Cell, Tissue and Organ Culture (PCTOC) - In vitro regeneration of date palm (Phoenix dactylifera L.) plants through somatic embryogenesis leads to the generation of somaclonal variants. The...     

Growth and Physiology of Maize (Zea mays L.) in a Nickel-Contaminated Soil and Phytoremediation Efficiency Using EDTA

Journal of Plant Growth Regulation - Nickel (Ni) element is strongly phytotoxic at high concentrations for several plants, but due to its dual behavior and complicated chemistry, it has received...