First chemical synthesis of a scorpion alpha-toxin affecting sodium channels: the Aah I toxin of Androctonus australis hector.

Aah I is a 63-residue alpha-toxin isolated from the venom of the Buthidae scorpion Androctonus australis hector, which is considered to be the most dangerous species. We report here the first chemical synthesis of Aah I by the solid-phase method, using a Fmoc strategy. The synthetic toxin I (sAah I) was renatured in DMSO-Tris buffer, purified and subjected to thorough analysis and comparison with the natural toxin. The sAah I showed physico-chemical (CD spectrum, molecular mass, HPLC elution), biochemical (amino-acid composition, sequence), immunochemical and pharmacological properties similar to those of the natural toxin. The synthetic toxin was recognized by a conformation-dependent monoclonal anti-Aah I antibody, with an IC50 value close to that for the natural toxin. Following intracerebroventricular injection, the synthetic and the natural toxins were similarly lethal to mice. In voltage-clamp experiments, Na(v) 1.2 sodium channel inactivation was inhibited by the application of sAah I or of the natural toxin in a similar way. This work describes a simple protocol for the chemical synthesis of a scorpion alpha-toxin, making it possible to produce structural analogues in time.     

Macroecology of Aquatic Insects: A Quantitative Analysis of Taxonomic Richness and Composition in the Andes Mountains of Northern Ecuador

To determine the spatial dynamics of Neotropical lotic insect species, specimens were collected from 41 streams on the eastern and western flanks of the Andes Mountains in Ecuador. We examined the manner in which taxonomic richness and composition differed with elevation, latitude, and versant. Statistical analyses were limited to 5 families (Ephemeroptera: Baetidae, Leptohyphidae, Oligoneuriidae; Heteroptera: Naucoridae; Coleoptera: Elmidae), comprising 32 genera and 85 species, for which identifications or morphospecies assignments were reliable. Assessment of taxonomic diversity was based on the richness of genera and species at each site. In addition, each site was characterized by species richness within each of 4 families with more than 10 species. The effects of versant and transect on composition and structure were family‐specific. Mean site differences between versants in elmid richness at generic and specific levels depended on transect. Only baetid richness was affected by versant and transect in a consistent manner. Variation among sites in composition based on all genera and species was captured using multidimensional scaling (MDS). Subsequent MANOVAs based on scores from MDS axes revealed that differences between versants were much stronger in the southern transect, although transects differed from each other at specific and generic levels. A Jaccard's similarity matrix was computed for each family to reflect the spatial organization of taxonomic composition. Mesogeographic patterns of species composition for each of the four families were correlated (Mantel analysis) at both the regional level and at the level of the entire study area. At the regional level, the only pair of families to exhibit correlated patterns of species composition was elmids and naucorids in the southwestern region. The pattern of species composition for each family was correlated with the patterns for one or more other families at the level of the entire study area. Thus, spatial dynamics of species composition was similar for the families examined, suggesting that the Andes exert a consistent influence on species distributions within families, regardless of ordinal affiliation. At a local scale, however, the way in which taxonomic composition changed with latitude and versant was family‐specific. Mayflies, the most vagile of the taxa studied, had the highest percentage of species overlap between versants. Of three genera of Naucoridae collected, species of Ambrysus, of probable Mexican origin, were found only on the eastern versant, corroborating other evidence that the genus is recent in South America. Moreover, dispersion by Ambrysus across the Andes Mountains may not have occurred, as it has for Cryphocricos and Limnocoris, which are of probable South American origin.     

Crystal structure of the collagen alpha1(VIII) NC1 trimer.

Collagen VIII is a major component of Descemet's membrane and is also found in vascular subendothelial matrices. The C-terminal non-collagenous domain (NC1) domain of collagen VIII, which is a member of the C1q-like protein family, forms a stable trimer and is thought to direct the assembly of the collagen triple helix, as well as polygonal supramolecular structures. We have solved the crystal structure of the mouse alpha1(VIII)(3) NC1 domain trimer at 1.9 A resolution. Each subunit of the intimate NC1 trimer consists of a ten-stranded beta-sandwich. The surface of the collagen VIII NC1 trimer presents three strips of partially exposed aromatic residues shown to interact with the non-ionic detergent CHAPS, which are likely to be involved in supramolecular assemblies. Equivalent strips exist in the NC1 domain of the closely related collagen X, suggesting a conserved assembly mechanism. Surprisingly, the collagen VIII NC1 trimer lacks the buried calcium cluster of the collagen X NC1 trimer. The mouse alpha1(VIII) and alpha2(VIII) NC1 domains are 71.5% identical in sequence, with the differences being concentrated on the NC1 trimer surface. A few non-conservative substitutions map to the subunit interfaces near the surface, but it is not obvious from the structure to what extent they determine the preferred assembly of collagen VIII alpha1 and alpha2 chains into homotrimers.     

Biotransformation of organic sulfides. Part 9. Formation of (S) para-substituted phenyl methyl sulfoxides by biotransformation usingHelminthosporium species NRRL 4671

Phenyl methyl sulfides substituted in thepara position with methyl, fluoro, chloro, bromo, cyano, nitro, amino, acyl, methoxy, thiomethyl and methylsulfinyl groups have been converted to (S) sulfoxides by biotransformation usingHelminthosporium species NRRL 4671. The highest yields and enantiomeric excesses were obtained with bromo, cyano, methoxy, thiomethyl and methylsulfinyl substituents and in two cases (para-Br and -CN) the products could be crystallized to give (S) sulfoxide of ≥ 96% ee.     

Nitric oxide does not promote iron release from ferritin

It has been previously reported that iron release from ferritin could be promoted by nitric oxide (NO) generated from sodium nitroprusside. It was thus proposed that some of the toxic effects of NO could be related to its ability to increase intracellular free iron concentrations and generate an oxidative stress. On the contrary, the iron exchange experiments reported here show that NO from S-nitrosothiols is unable to promote iron release from ferritin. The discrepancy may be explained by the disregarded ability of ferrozine, the ferrous trap used in the previous report, to mobilize iron both from ferritin and from sodium nitroprusside spontaneously.     

Stomatal and nonstomatal limitations of photosynthesis in relation to the drought and shade tolerance of tree species in open and understory environments

 Light saturated photosynthesis (A) in field saplings of shade tolerant, intermediate, and intolerant tree species was analyzed for stomatal and nonstomatal limitations to test differences between species and sun and shade phenotypes during drought. Throughout the study, photosynthesis was highest and mesophyll limitations of A (L_m) lowest in the intolerant species in both open and understory habitats. The shade tolerant species exhibited the only drought-related decreased A and increased L_m in the open, and the greatest drought-related decreased A and increased L_m in the understory. Few species exhibited significant habitat or drought-related differences in stomatal conductance to CO₂ (g_c), but even slight decreases in g_c during drought were associated with large increases in stomatal limitations to A (L_g). Combined changes in L_m and L_g resulted in increased relative stomatal limitation to A (l _g) in several species during drought. Nevertheless, the overall lack of stomatal closure allowed for nonstomatal limitations to play a major role in reduced A during drought. Higher leaf N was associated with shallower slope of the l _g versus g_c relationship, an indication of greater A capacity. Photosynthetic capacity tended to be greater in the intolerant species than the tolerant species, and it tended to decrease during drought primarily in the shade tolerant species in the understory. Findings in the literature suggest that carbon reduction reactions may be more susceptible to drought than photosynthetic light reactions. If so, reduced carbon reduction capacity of shade tolerant species or shade phenotypes may predispose them to drought conditions, which suggests a mechanism behind the well-recognized tradeoff between drought tolerance and shade tolerance of temperate tree species. Received: 20 October 1995 / Accepted: 20 February 1996