The proline-activating activity of the multienzyme gramicidin S synthetase 2 can be recovered on a 115-kDa tryptic fragment

The multienzyme gramicidin S synthetase 2 was treated with trypsin to obtain fragments capable of activating proline. Three different active fragments were detected. The course of proteolysis was simulated by using a concentration range of trypsin; the cleavage pattern indicated that one of the fragments was particularly stable. This fragment was purified and shown to have a molecular mass of 115 kDa. It was compared chromatographically, by SDS/PAGE, and enzymatically to a Pro-activating fragment produced by a gramicidin-S-negative mutant. It can be concluded that the proteolytic fragment represents a structure which is contained on a continuous part of the polypeptide chain of gramicidin S synthetase 2 and has a relatively compact structure. This provides evidence that the multienzyme gramicidin S synthetase 2 is, at least in part, constructed from functional domains. An approach towards extending these studies to other parts of the gramicidin S synthetase 2 molecule has also been devised. This work complements recombinant DNA studies in the area, providing stable functional fragments.     

Proteolytic processing in a non-lysosomal compartment is required for transcytosis of protein-polylysine conjugates in cultured Madin-Darby canine kidney cells

The transcytosis of horseradish peroxidase, as well as its poly(L-lys) and poly(D-lys) thioether conjugates, was investigated in Strain I Madin-Darby canine kidney (MDCK) cell monolayers grown on 0.4 microns pore size polycarbonate membranes in Costar Transwells. The 3 types of HRP had almost identical rates of transport during the first 2 hr of incubation. However, a significant increase of basal-to-apical transport was detected beginning at 3 hr only in Transwells containing the poly(L-lys) conjugate. This increase was inhibited by colchicine (2 microM) and by the Bowman-Birk protease inhibitor (0.1 mg/ml), but not by NH4Cl (10 mM) or chloroquine (0.1 mM). The increase was abolished either by prior trypsinization of the conjugate or by incubation at 4 degrees C. Ultrafiltration studies indicated that the transcytosed poly(L-lys) conjugate was smaller in size than the original conjugate. These results indicate that the conjugate was processed during transcytosis in a non-lysosomal proteolytic compartment, where its poly(L-lys) moiety was selectively degraded, allowing active peroxidase to be released into the apical medium.     

The contribution of symbiotic yeast to toxin resistance of the cigarette beetle (Lasioderma serricorne)

Representative plant allelochemicals were tested for toxicity to larvae of the cigarette beetle Lasioderma serricorne (F.) that were either untreated, treated with fungicides, or treated to render them free of symbiotic yeast (aposymbiotic) through surface sterilization of eggs. Insects rendered symbiont-free had higher mortality and/or developmental rates than controls when fed diets containing flavone, resorcinol or tannic acid. Fungicides reduced symbiont populations and/or caused morphological abnormalities. Two hydrolytic enzymes, which made up a significant protion of mycetome hydrolytic activity, were absent when symbionts were not present, as indicated by gel electrophoresis. This information indicates symbionts do contribute to the survival of their host by detoxifying toxins.

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Résumé La toxicité relative de substances allélochimiques végétales typiques a été examinée sur des larves de L. serricorne F. traitées aux fongicides et rendues aposymbiotiques par stérilisation superficielle des ufs. La toxicité de la nicotine est relativement inaffectée chez les larves aposymbiotiques; cependant les toxicités des resorcinol, flavone et acide tannique sont significativement augmentées chez les insectes ayant reçu un traitement pour éliminer leurs symbiontes. L'électrophorèse sur gel a montré que quelques enzymes responsables de l'hydrolyse du 1-naphthyl acétate, réaction enzymatique de la détoxification enzymatique, sont absentes chez les insectes aposymbiotiques. L'acide sorbique a réduit significativement l'effectif de symbiontes, tandis que le bénomyl a réduit leur gamme provoquant la multiplication anormale d'autres espèces. Ces résultats montrent que les symbiontes contribuent aux possibilités de détoxification de l'insecte. L'élimination des symbiontes peut être une technique efficace pour lutter contre les insectes qui en contiennent, puisqu'elle les priverait de leur contribution à l'alimentation et à la détoxification. Cette stratégie est vraisemblablement compatible avec des programmes de lutte intégrée, puisque les prédateurs et parasites ne contiennent pas de symbiontes.

     

农业部召开全国农业学校植物生态学教学讨论会

我国现有地区以上中等农业学校224所,分布全国各地,担负着全国中级农业科技人才的培养和县以下在职农业技术干部的轮训任务。实践证明,中等农业学校是我国初、高级农业教育和研究机构中承上启下的组成部分,是加速农业现代化建设的重要方面军。中等农业学校教育质量的高低,与专业基础课——植物及植物生理学教学质量的好坏是密切相关的。1980年5月农业部教育局颁布《植物及植物生理教学大纲》的     

Retardation of leaf senescence by inhibitors of RNA and protein synthesis

Effects of actinomycin-D (ACT), cycloheximide (CH), rifampicin (RIF) and chloramphenicol (CAP) on senescence of soybean leaf discs were investigated. All inhibitors tested are effective in retarding senescence of soybean leaf discs. However, CH is more effective than ACT, RIF and CAP, suggesting that activation of preexisting, latent metabolic systems present in the cytoplasm piays predominant role in the initiating of leaf senescence. However, the possibility that events taking place in the nucleus or chloroplast are essential for the initiation of leaf senescence cannot be excluded.     

Intracellular pH controls protein synthesis rate in the sea urchine egg and early embryo.

Direct comparisons between intracellular pH and protein synthesis in the sea urchin egg and early embryo show that pH controls protein synthesis rate in a highly sensitive and reversible manner. The entire increase and maintenance of protein synthesis at fertilization or parthenogenetic activation could be accounted for by a permanent increase in intracellular pH. However, unfertilized eggs whose intracellular pH has been raised artificially by ammonia take at least 30 min longer to reach the rate of protein synthesis seen in fertilized eggs. This time lag for ammonia activation and the decrease in protein synthesis rate during mitosis suggest that other unknown factors can also influence protein synthesis rate during fertilization and early embryogenesis.     

Light Effects in Yeast: Evidence for Participation of Cytochromes in Photoinhibition of Growth and Transport in Saccharomyces cerevisiae Cultured at Low Temperatures

Visible light of moderate intensity inhibits growth, respiration, protein synthesis, and membrane transport in bakers' yeast and has a deleterious effect on membrane integrity. The results of this study indicate that these effects require the presence of cytochromes b and a/a(3). The light sensitivities of growth rate and [(14)C]histidine uptake in wild-type rho(+) Y185 and D225-5A strains of Saccharomyces cerevisiae were compared with those in a variety of mutants lacking cytochrome b or a/a(3) or both; a close correlation was found between the presence of these respiratory pigments and photosensitivity. Thus, strain TL5-3C, a nuclear petite lacking cytochromes b, a, and a(3), was resistant to light; strain GL5-6A, another nuclear petite having reduced amounts of cytochromes a and a(3), was partially resistant; strains MB127-20C and MB1-6C, nuclear petites lacking only cytochrome b, were also only partially resistant to light; whereas mutants containing all three cytochromes but having their respiratory chain either nonfunctional (strain ZK3-6B) or uncoupled (strain 18-27/t12) were fully sensitive to light. Finally, an equal-energy, broad-band action spectrum for the light inhibition of growth and transport indicated that blue light (408 nm) was most effective; these wavelengths correspond to the Soret region of the cytochrome absorption spectrum. The results suggest, therefore, that the yeast cytochromes b, a, and a(3) are the primary photoreceptors for the inhibitory effects of light and, perhaps, for other processes, such as the entrainment of biological rhythms in this species.     

Comparative ultrastructure of Mycobacterium leprae and Mycobacterium lepraemurium cell envelopes.

The structural properties of the cell envelopes of Mycobacterium leprae and Mycobacterium lepraemurium were investigated by freeze-fracture, freeze-etching, and negative-staining techniques. Freeze-fracture split the cell wall and exposed the internal features of the peptidoglycolipid mycosidic filamentous network. The cell membrane was also split into two asymmetric faces. The external fracture face was characterized by linear arrays of intramembranous particles, whereas the protoplasmic fracture face showed randomly distributed clusters of particulate entities. Comparative analysis of the ultrastructural features observed in M. leprae and M. lepraemurium indicated that the organization of the cell envelope in these two species differed particularly with respect to the amount and complexity of the superficial peptidoglycolipid and mycosidic integument, which is poorly developed in the mycobacterium responsible for human disease.