Redox-controlled,in vivo and in vitro phosphorylation of the α subunit of the light-harvesting complex I in Rhodobacter capsulatus

Labelling of Rhodobacter capsulatus cells with (³²P)Pi in a phototrophic culture results in phosphorylation of a membrane-bound polypeptide identified as the subunit of the LHI antenna complex of the photosynthetic apparatus. Phosphorylation of the same polypeptide was also observed by incubation of chromatophores with (³²P)ATP or under conditions of photophosphorylation with ADP and (³²P)Pi. The identity of the phosphorylated LHI- subunit was demonstrated by N-terminal protein sequencing of the phosphorylated polypeptide and by failure of labelling in LHI-defective mutants. Pre-aeration of the samples or addition of the oxidant potassium ferrcyanide stimulated the kinase activity whereas the presence of soluble cytoplasmic proteins impaired phosphorylation in an in vitro assay. No effect resulted from addition of reductants to the assay medium. The results indicate the presence of a membrane-bound protein kinase in R. capsulatus that phosphorylates the subunit of the LHI antenna complex under redox control.Abbreviations Pi inorganic phosphate - SDS-PAGE sodium dodecyl-sulfate polyacrylamide gel electrophoresis     

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.     

Purification and Properties of Manganese Superoxide Dismutase from Norway Spruce (Picea abies L. Karst)

A manganese-containing superoxide dismutase (SOD; EC 1.15.1.1 [EC] )was purified to electrophoretic homogeneity from seeds of Norwayspruce (Picea abies L.). The apparent molecular mass of thepurified enzyme was 86 kDa, as determined by gel filtration.The subunit molecular mass, estimated by SDS-polyacrylamidegel electrophoresis, was 22 kDa both in the presence and inthe absence of 2-mercaptoethanol. Thus, the native enzyme isa homotetramer with subunits that were not linked by disulfidebonds. The isoelectric point of this Mn-SOD was 5.5. The specificactivity of the Mn-SOD was strongly pH-dependent and was 400units per nmol SOD at pH 7.8 and 30 units per nmol SOD at pH10.4. The first 25 amino acid residues in the amino terminalregion of spruce Mn-SOD exhibited a high degree of sequencehomology to those of Mn-SODs from other organisms. In Mn-deficientneedles the activity of Mn-SOD was only half of that in non-deficientneedles, whereas the activity of CuZn-SOD was doubled. (Received May 20, 1994; Accepted October 31, 1994)     

A procedure for securing large and undisturbed soil cores for field simulation studies

Summary Dynamic load is a technique which can be used to secure large pedons successfully in duplex profiles with massive clay B horizons. Data show that soil profiles obtained by this method have minimum change in soil physical properties including structure and compaction. The work reported here is part of that submitted as a requirement for the Ph. D. at the University of New England by the senior author.     

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.     

Muscular sarcosporidiosis in the common European weasel, Mustela nivalis.

Muscular sarcosporidiosis is reported for the first time in the common European weasel, Mustela nivalis. The morphology of the sarcocysts is described from fresh and stained histological preparations. Attempts to complete the sexual cycle of this mustelid parasite in a tawny owl, Strix aluco, are reported and the results discussed in the light of hypothetically likely sources of infection with muscular sarcosporidiosis for carnivores or omnivores, including man and other primates.