Larvicidal activities of limonoids from Turraea abyssinica (Meliaceae) on Tuta absoluta (Meyrick)

Preliminary screening of extracts of the leaves and stems of four Turraea plant species (Meliaceae) on second instar larvae of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) showed that the methanolic extract of Turraea abyssinica leaves possess good toxic potential with LD₅₀ of 270.7 ppm. Fractionation of this extract led to isolation of a new limonoid derivative, 12α‐diacetoxywalsuranolide (1) and three other known limonoids [1α,7α,12α‐triacetoxy‐4α‐carbomethoxy‐11β‐hydroxy‐14β,15β‐epoxyhavanensin (2), 11‐epi‐21‐hydroxytoonacilide (3), 11β,12α‐diacetoxycedrelone (4)]. The structures of the compounds were established by IR, UV, mass spectrometry and 1D/2D NMR analyses, and in the case of the known compounds, also by comparison with reported data. All the isolates were tested for their larvicidal activities at different dose range against second instar larvae of T. absoluta. They were found to be more active (with LD₅₀ < 7.0 ppm) compared to the reference compound azadirachtin (LD₅₀ value of 7.8 ppm).     

Cleome monophylla essential oil and its constituents as tick (Rhipicephalus appendiculatus) and maize weevil (Sitophilus zeamais) repellents

The repellency of the essential oil of the shrubCleome monophylla (Family: Capparidaceae) and identified constituents of the oil were evaluated against the livestock tick,Rhipicephalus appendiculatus and the maize weevil,Sitophillus zeamais. In a tick climbing repellency bioassay, the oil ofC. monophylla exhibited repellency which, at the highest dose, was comparable to that of the commercial arthropod repellent N,N-diethyl toluamide (DEET). In a Y-tube olfactometer bioassay,C. monophylla oil showed higher or comparable repellency againstS. zeamais relative to DEET at all the doses tested. 14 Compounds were identified in theC. monophylla oil by GC, GC-MS and coinjection with authentic samples. Terpenolene was found to occur in largest quantity (14%) followed by 1-α-terpeneol (10%), pentacosane (9%), (α+β)-humulene (8%), phytol (5%) and 2-dodecanone (4%). The most repellent components againstR. appendiculatus andS. zeamais were 1-α-terpeneol and 2-dodecanone. The overall pattern of repellency activity of theC. monophylla constituents with respect to the two arthropods was, however, different. The potential ofC. monophylla in tick and maize weevil control is discussed.     

Association of the yeast poly(A) tail binding protein with translation initiation factor eIF-4G.

Although the cap structure and the poly(A) tail are on opposite ends of the mRNA molecule, previous work has suggested that they interact to enhance translation and inhibit mRNA degradation. Here we present biochemical data that show that the proteins bound to the mRNA cap (eIF-4F) and poly(A) tail (Pab1p) are physically associated in extracts from the yeast Saccharomyces cerevisiae. Specifically, we find that Pab1p co-purifies and co-immunoprecipitates with the eIF-4G subunit of eIF-4F. The Pab1p binding site on the recombinant yeast eIF-4G protein Tif4632p was mapped to a 114-amino-acid region just proximal to its eIF-4E binding site. Pab1p only bound to this region when complexed to poly(A). These data support the model that the Pablp-poly(A) tail complex on mRNA can interact with the cap structure via eIF-4G.     

Involvement of N-acyl-l-homoserine lactone autoinducers in controlling the multicellular behaviour of Serratia liquefaciens

Several bacterial species possess the ability to differentiate into highly motile swarmer cells capable of rapid surface colonization. In Serratia liquefaciens, we demonstrate that initiation of swarmer-cell differentiation involves diffusible signal molecules that are released into the growth medium. Using high-performance liquid chromatography (HPLC), high resolution mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy, we identified N-butanoyl-l -homoserine lactone (BHL) and N-hexanoyl-l -homoserine lactone (HHL) in cell-free Serratia culture supernatants. BHL and HHL are present in a ratio of approximately 10:1 and their structures were unequivocally confirmed by chemical synthesis. The swrlswarmer initiation) gene, the predicted translation product of which exhibits substantial homology to the Luxl family of putative Nacyl homoserine lactone (AHL) synthases is responsible for directing synthesis of both BHL and HHL. In an swrl mutant, swarming motility is abolished but can be restored by the addition of an exogenous AHL. These results add swarming motility to the rapidly expanding list of phenotypes known to be controlled through quorum sensing.     

The Ethics of Medical Practitioner Migration From Low-Resourced Countries to the Developed World: A Call for Action by Health Systems and Individual Doctors

Medical migration appears to be an increasing global phenomenon, with complex contributing factors. Although it is acknowledged that such movements are inevitable, given the current globalized economy, the movement of health professionals from their country of training raises questions about equity of access and quality of care. Concerns arise if migration occurs from low- and middle-income countries (LMICs) to high-income countries (HICs). The actions of HICs receiving medical practitioners from LMICs are examined through the global justice theories of John Rawls and Immanuel Kant. These theories were initially proposed by Pogge (1988) and Tan (1997) and, in this work, are extended to the issue of medical migration. Global justice theories propose that instead of looking at health needs and workforce issues within their national boundaries, HICs should be guided by principles of justice relevant to the needs of health systems on a global scale. Issues of individual justice are also considered within the framework of rights and social responsibilities of individual medical practitioners. Local and international policy changes are suggested based on both global justice theories and the ideals of individual justice.