Structural studies on glycolipids. Part 1: 220 MHz pmr spectra of acetylated galactocerebrosides

The pmr spectra of fully acetylated 2S: 3R-2 amino-trans-4 octadecene-1, 3 diol (sphingosine) (lb), 2S : 3R-2 aminooctadecane-1, 3 diol (dihydrosphingosine) (2b), 1-O-β-D-galactopyranosyl-2S : 3R-2 tetracosanoylamido-trans-4 octadecene-1, 3 diol (cerasine) (3b), and 1-O-β-D-galactopyranosyl-2S : 3R-2 (2′ hydroxy) tetracosanoylamido-trans-4 octadecene-1, 3 diol (phrenosine) (4b), were determined in chloroform-d, acetone-d₆, and benzene-d₆ at 220 MHz. The relative chemical shifts of the various protons in the three solvents were different enough as to permit configurational and conformational information to be derived by partial first order analysis.     

Wiring diagrams of MAPK regulation by MEKK1, 2, and 3.

Mitogen-activated protein kinase (MAPK) pathways are activated by a plethora of stimuli. The literature is filled with papers describing the activation of different MAPKs by almost any stimulus or insult imaginable to cells. In this review, we use signal transduction wiring diagrams to illustrate putative upstream regulators for the MAPK kinase kinases, MEKK1, 2, and 3. Targeted gene disruption of MEKK1, 2, or 3 defined phenotypes for each MEKK associated with loss of specific MAPK regulation. Genetic analysis of MEKK function clearly defines specific components of the wiring diagram that require MEKK1, 2, or 3 for physiological responses. We propose that signal transduction network wiring diagrams are valuable tools for hypothesis building and filtering physiologically relevant phenotypic responses from less connected protein relations in the regulation of MAPK pathways.     

Does Weeding Promote Regeneration of an Indigenous Tree Community in Felled Pine Plantations in Uganda?

The use of plantations to manage extensive tracks of deforested lands in the tropics is a conservation strategy that has recently received considerable attention. Plantation trees can promote seed dispersal by attracting dispersers and creating favorable site conditions, leading to increased germination and establishment of indigenous trees. Subsequently, plantation trees can be harvested for profit or left to senesce, leaving a native tree community. We evaluated the effect of vine, grass, and shrub cutting (weeding) over a 3‐year period on regeneration of indigenous trees subsequent to the removal of plantation softwoods in Kibale National Park, Uganda. Counter to what would be expected if weeding released trees from competition, we found no difference in the total number of stems or in the stems greater than 10 cm diameter at breast height between control and weeded plots; there were more stems greater than 1 cm diameter at breast height in the control plots. For species found in both control and weeded plots, the maximum size of individuals did not differ. At the end of the study, 61 species were found in the control plots and 43 species were found in the weeded plots, and in both types of plots the three most abundant species were the same. The number of species and stems classified as early or middle successional species did not differ between weeded and control plots. The fact that weeding did not promote regeneration of indigenous trees after the removal of plantation trees illustrates the importance of evaluating and field‐testing potential management options.     

Hybrid formation within the genus Leishmania?

Leishmanial organisms isolated from a desert rodent (Psammomys obesus) and a feral dog (Canis familiaris) in the Eastern Province of Saudi Arabia were isoenzymically distinct from Leishmania major and L. arabica, organisms usually associated with human and wild animal cutaneous leishmaniasis in this area. Further examination of isoenzyme banding patterns of cloned populations of these organisms, together with karyotyping using orthogonal field alternation gel electrophoresis and the use of highly specific kinetoplast DNA probes, has produced evidence suggesting that these organisms isolated from the dog and the rodent are hybrids of L. major and L. arabica.     

Methods of tracing hydrogen in polyketide biosynthesis: High field NMR spectroscopy of citrinin produced in a D2O based medium

Penicillium citrinum cultures have been germinated on an H₂O-based medium, resuspended on a D₂O-based medium and treated with [l,2-¹³C₂] acetate. The resulting citrinin (1) has been analysed by²H and¹³C nuclear magnetic resonance spectroscopy and information about the metabolism of hydrogen in citrinin biosynthesis has been deduced.