Absorption of light in photoreceptors: Effect of waveguiding property

The effect of waveguiding property (i.e., the intensity distribution) of the photoreceptor on the number of photons absorbed in a photoreceptor has been studied. It has been found that the effect is significant only for large values of the exposure and the maximum effect is less than 11% in the case of human rod photoreceptor. In the analysis, the funnelling effect, which follows from the coupling between the interior and exterior fields, has not been considered.Work partially supported by the Department of Science and Technology (India)B. D. Gupta is associated with the School of Bioscience Studies     

Design,synthesis, characterization,antibacterial and antifungal activities of a novel class of 5,7-diaryl-4,4-dimethyl-4,5,6,7-tetrahydropyridino[3,4-d]-1,2,3-selenadiazoles

Compound 26 is more potent against Escherichia coli. and 24 is more active against Staphylococcus aureus, β-Heamolytic streptococcus, Vibreo cholerae, Salmonella typhii, and Shigella flexneri than the standard drug ciprofloxacin. Moreover, of all the compounds tested, 26 is more effective against Aspergillus flavus and Mucor, than the standard drug fluconazole.     

Antibacterial Agents in Mediterranean Finfish Farming: A Synopsis of Drug Pharmacokinetics in Important Euryhaline Fish Species and Possible Environmental Implications

The literature pertaining to the use of registered antibacterial agents in Mediterranean finfish farming is reviewed, with an emphasis on the Greek fish-farming industry. This review provides a scientific resource dedicated to the design of future antibacterial dosing regimes in Mediterranean fish farming, where insufficient supporting information is currently available. This paper addresses the paucity in knowledge concerning pharmacokinetics and the efficacy and environmental impact of commonly used antibacterials needed to direct future research and promote good practices in the euryhaline fish farming industry. Several registered antibacterials are currently available for combating bacterial infections, including tetracyclines, (fluoro) quinolones, potentiated sulfa, penicillin and chloramphenicol derivatives. Based on the available data, oxytetracycline (OTC) and quinolone drugs (oxolinic acid – OA and flumequine – FLU) are the most widely used in Mediterranean aquaculture. As a result these drugs have received the most extensive studies, whereas, there is considerable paucity of reliable data on pharmacokinetic and the depletion characteristics of other drugs used, particularly potentiated sulfa, penicillin derivatives and florfenicol. We find there is incomplete data on drug efficacy and minimum inhibitory concentrations (MIC) for common antibacterials used against the major bacterial pathogens of Mediterranean fish species. Furthermore, a considerable lack of data on environmental drug concentrations around Mediterranean fish farms was also identified, highlighting the need for more extensive environmental studies to monitor contamination in environmental components i.e., water and sediment, and in non-target species (flora and fauna). Prudent selection and use of antibacterials can encourage lower dosage applications, enhance treatment efficacy, and help to minimize contamination of the environment. Selection of readily bioavailable drugs which have low environmental persistence, low aquatic toxicity and high antibacterial efficacy is advised, to reduce potential losses to the environment and associated toxic effects on target species and the development of bacterial resistance. Lack of present data made it impossible to provide thorough and accurate guidance on selection and use of antibacterials and approaches for minimizing environmental impacts for the treatment of major euryhaline aquaculture species.     

华北地区针叶林下凋落物层化学性质的研究

森林凋落物中贮积了大量的有机、无机养分物质,它是森林土壤自然肥力的重要来源之一。在森林生态系统中,养分物质的内部循环主要是通过凋落物来实现的。在分解、转化过     

Detection of cellular responses to toxicants by dielectrophoresis

The dielectrophoretic (DEP) crossover method has been applied to the detection of cell responses to toxicants. Time and dose responses of the human cultured leukemia (HL-60) line were measured for paraquat, styrene oxide (SO), N-nitroso-N-methylurea (NMU) and puromycin. These toxicants were chosen because of their different predominant mechanisms of action, namely membrane free radical attack, simultaneous membrane and nucleic acid attack, nucleic acid alkylation, and protein synthesis inhibition, respectively. For all treatments, the specific membrane capacitance (C_mem) of the cells decreased while the specific membrane conductance (G_mem) increased in dose- and time-dependent manners. The DEP responses correlated sensitively with alterations in cell surface morphology, especially folds, microvilli, and blebs, observed by scanning electron microscopy. The DEP method was more sensitive to agents that had a direct action on the membrane than to agents for which membrane alterations were secondary. The responses to paraquat and SO, which directly damaged the cell membrane, could be detected 15 min after exposure, while those for puromycin and NMU, which acted on intracellular targets, could be detected after 30 min. The detection times and dose sensitivity results showed that the DEP method is much faster and more sensitive than conventional cell and higher organism viability testing techniques. The feasibility of producing small instruments for toxicity detection and screening based on cellular dielectric responses is discussed.     

Length, mass, and denaturation of double-stranded RNA molecules compared with DNA

The contour lengths of linear, double-stranded (ds) RNAs from mycovirus PcV and Pseudomonas bacteriophage ø6 have been measured with samples prepared for the electron microscope from 0.05 to 0.5 M NH₄Cl solutions. A linear dependence of contour length on the logarithm of ionic strength was found and compared with that of dsDNA (pBR322, linearized and open-circular forms). Conditions for molecular weight determinations of any natural dsRNA by electron microscopy have been established, and the method has been calibrated with ø6 dsRNA of known nucleotide sequence. The results imply that dsRNA in 0.20 M NH₄Cl solution has a rise per basepair of 0.271 nm, which is shorter than that in the A-conformation (4%) and in the A′-conformation (10%). The thermal behavior of dsRNA in terms of melting temperature and exhibition of fine structure of melting curves was found to be generally similar to that of dsDNA, as expected from the literature. Folding of dsRNA in ethanolic solution was similar to that of dsDNA. However, in contrast to dsDNA, coiled coils could not be induced by ethanol, which is consistent with dsRNA being stiffer than dsDNA. Concerning dsDNA, the results show that a contraction in rise per basepair by 0.1 nm is coupled with an increase in the winding angle between basepairs by 0.47°, as qualitatively predicted by polyelectrolyte theory.     

柞蚕抗菌肽D中精氨酸、赖氨酸和色氨酸等氨基酸残基的化学修饰

用不同的化学试剂修饰了柞蚕抗菌肽D分子中的色氨酸、精氨酸和赖氨酸等氨基酸残基。NBS修饰抗菌肽D,以及氨肽酶M对抗菌肽D作用的结果表明色氨酸残基对抗菌肽D抑制E.coli D31的作用影响不大。CHD和MLH对精氨酸和赖氨酸残基的修饰,导致抗菌肽D失去抑制E.coli的作用,但可逆地消除CHD和MLH的修饰作用后,抗菌肽D恢复了对E.coli D31的抑菌作用。这些结果初步认为,抗菌肽D抑菌作用与分子中的荷电性有关,改变了分子的电荷,也就同时失去了其抑菌功能。 此外,对精氨酸残基修饰的结果还表明,抗菌肽D的免疫原性与精氨酸残基有关。但是,抗菌肽D的免疫决定簇与其生物活性中心并不完全平行。     

Electrical tolerance (breakdown) of theChara corallina plasmalemma: II. Inductive property of membrane and effects of pH o and impermeable monovalent cations on breakdown phenomenon

Summary Changes in the chord conductanceG and the membrane electromotive forceE _m in the so-called breakdown region of large negative potential of theChara plasmalemma were analyzed in more detail. In addition to the increase inG, the voltage sensitivity of the change inG increased, which was the cause of marked inductive current in the breakdown region. The breakdown potential, defined as a critical potential at which both low and high slope conductances of theI–V _m relationship cross, almost coincided with the potential at which an inductive current began to appear. This breakdown potential level changed with pH _o in a range between 5 and 9. TheChara plasmalemma was electrically most tolerant around pH _o 7.In some cellsE _m shifted to a positive level as large as +50+70 mV during the breakdown phenomenon. Such a large positive shift ofE _m is caused mainly by the increase in conductance of Cl^– and partly Ca²⁺ and K⁺.