Somatic polyploidy in extraembryonic membranes of the snake,Elaphe guttata

Summary Video-densitometric DNA measurements of Feulgenstained tissues of 42 day old eggs of the corn snake,Elaphe g. guttata (Columbridae, Serpentes), revealed a basic DNA content of 2C=2.17 pg, with somatic polyploidy in the allantois, the chorioallontois, the yolk sac, and other extraembryonic membranes. The maximum value determined was 128C (in binucleate cells 2×128C) at the distal pole of the egg. This is the first report of somatic polyploidy in a snake, and one of the first in reptiles in general.     

Intra- and interspecific host discrimination in Asobara (Hymenoptera) larval endo-parasitoids of Drosophilidae: Comparison between closely related and less closely related species

Host discrimination studies were conducted with different species of Asobara, which are larval endo-parasitoids of Drosophilidae. Results indicated variable host discrimination which depended on the relatedness of the species. The closely related sibling species Asobara tabida (Nees) and A. rufescens (Foerster) were not only capable of intraspecific discrimination, but also avoided multiparasitism by discriminating between unparasitized host larvae and larvae previously parasitized by females of the other species. This ability to discriminate interspecifically does not seem functional as each species occupies its own microhabitat. As it was shown to be absent in less closely related Asobara species we concluded that interspecific discrimination by A. tabida and A. rufescens was due to their close relationship.     

Identification of substrate and effector binding sites of phosphoenolpyruvate carboxylase from Crassula argentea. A possible role of phosphoenolpyruvate as substrate and activator

Phosphoenolpyruvate carboxylase (EC 4.1.1.31) purified from leaves of the crassulacean acid metabolism plant (Crassula argentea) was chemically modified by the specific arginyl reagent 2,3-butanedione. Modification resulted in enzyme inactivation which followed pseudo first-order kinetics. Participation of arginyl residues involved in the binding of or response to both phosphoenolpyruvate and malate, respectively, was established. Inactivation and protection studies suggest the presence of three sites involved in the binding of the substrate, phosphoenolpyruvate, the activator, glucose 6-phosphate, and the inhibitor, malate. Studies using both fluorescence measurements of binding and steady-state kinetic methods indicate that phosphoenolpyruvate can bind both to the active site and to the activator site. Evidence for stimulation of the activity of phosphoenolpyruvate carboxylase upon the binding of substrate to the activation site was provided by kinetic studies using AMP, previously shown to be a specific ligand for the activation site.     

Skull molding caps: an adjunct to craniosynostosis surgery

External cranial vault molding using dynamic splinting is an adjunct to surgery in the treatment of craniosynostosis skull deformities. The skull molding cap not only maintains desired skull form, but also provides further active molding to normalize skull shape. Dynamic skull remodeling from these devices occurs primarily by translational movements of bone. Traction and compression result in bony repositioning which allows further reshaping as the osteoblasts and osteoclasts respond to these stresses. Three basic designs have been described. In practice, each one must be modified to meet individual needs, and adaptations are made according to established principles of dynamic splinting.     

Light-regulated methylation of chloroplast proteins

Protein carboxyl methyltransferases, which catalyze transfer of methyl groups from S-adenosyl-L-methionine to the free carboxyl groups of acidic amino acids in proteins, can be divided into two classes based on several characteristics, such as the stoichiometry of substrate protein methylation, base stability of the incorporated methyl group, specificity for substrate, and participation in a regulatory system with which methylesterases are associated. The presence of such an enzyme in a photosynthetic system was demonstrated in the present work. The extent of methylation of chloroplast proteins was stimulated 30% by light and then decreased by the same amount in the presence of the electron transport inhibitor 3-(3',4'-dichlorophenyl)-1', 1'-dimethylurea or uncouplers of phosphorylation, indicating a dependence of the methyltransferase activity on photosynthetic electron transport and the trans-membrane delta pH. The light-independent, as well as the light-dependent, activity is probably of chloroplast origin since the extent of light stimulation in the purified thylakoid membranes and the stromal fraction was similar, and at low concentrations of S-adenosyl-L-methionine the small subunit of ribulose-1,5-bisphosphate carboxylase:oxygenase was found to be the predominant substrate. The labeling pattern of chloroplast proteins and labeling of an exogenous nonchloroplast protein indicated that the methyltransferase activity was not substrate-specific, although at low concentrations of the methyl donor, the small subunit of ribulose-1,5-bisphosphate carboxylase:oxygenase was labeled almost exclusively. Based on the low stoichiometry (less than 100 pmol/mg protein) of the methylation, its base lability, irreversibility, and the lack of substrate specificity except at very low concentrations of methyl donor, it was inferred that the chloroplast methyltransferase is best classified as a class II system that may function as part of a repair mechanism to replace racemized amino acids.     

Isolation of apical plasma membrane in rabbit gallbladder epithelium by Percoll density gradient centrifugation

The apical membranes of rabbit gallbladder epithelial cells were isolated by treating the homogenate with Ca2+ or Mg2+ and centrifuging the suspension in Percoll gradient. In this way brush-border membranes were obtained with enrichment factors ranging between 10 and 20 and yields of 15-30%. A second method is described with which membranes were isolated, without any preliminary treatment, first by differential centrifugation, then with Percoll gradient; the final membrane enrichment was over 15, however the yield was very low (3%). Many possible enzymatic markers of the apical plasma membrane were investigated: L-gamma-glutamyltransferase, alkaline phosphatase, leucine aminopeptidase, sucrase. The first appears to be that of choice. Apical membrane fraction could be also evidenced by autofluorescence or by labeling with Lotus tetragonolobus lectin. Preliminary experiments showed that apical plasma membranes isolated in this way form vesicles.     

Structural elements of bactopterin from Pseudomonas carboxydoflava carbon monoxide dehydrogenase

Bactopterin is a novel pterin occurring in bacterial molybdoenzymes as the organic portion of the molybdenum cofactor. Its structure is investigated here. The compound contains a single pterin ring and carries a side chain at carbon atom 6 of the pterin nucleus as indicated by the formation of pterin-6-carboxylic acid upon alkaline permanganate oxidation. Studies with phosphate-cleaving enzymes revealed the presence of two monophosphoric acid monoesters. The affinity of reduced bactopterin for thiol-Sepharose points to the presence of thiol(s) in active bactopterin.     

A process for protein enrichment of cassava by solid substrate fermentation in rural conditions

An artisanal static process for protein enrichment of cassava by solid-state fermentation, developed in laboratory and tested on pilot units in Burundi (Central Africa), provides enriched cassava containing 10.7% of dry matter protein versus 1% before fermentation. Cassava chips, processed into granules of 2-4-mm diameter, are moistened (40% water content) and steamed. After cooling to 40 degrees C, cassava is mixed with a nutritive solution containing the inoculum (Rhizopus oryzae, strain MUCL 28627) and providing the following per 100 g dry matter: 3.4 g urea, 1.5 g KH(2)PO(4), 0.8 g MgSO(4).7H(2)O, and 22.7 g citric acid. For the fermentation, cassava, with ca. 60% moisture content, is spread in a thin layer (2-3 cm thick) on perforated trays and slid into an aerated humidified enclosure. The incubation lasts +/- 65 h. The production of protein enriched cassava is 3.26 kg dry matter/m(2) tray. The effects of the variation of the nutritive solution composition and the inoculum conservation period on the protein production are equally discussed.     

Binding of the Bacillus sphaericus mosquito larvicidal toxin to cultured insect cells

Using both fluorescent labelled toxin and antibody--secondary antibody techniques, the Bacillus sphaericus toxin was found to bind strongly to susceptible Culex quinquefasciatus cells, but far less strongly to cells of insensitive insects. An insensitive clone of the C. quinquefasciatus cell line was discovered which bound toxin efficiently. The toxin was bound in the cold to sensitive cells and these cells could be rescued from cytotoxicity for ca. 15 min after warming, by which time toxin appeared to be internalized. Binding was saturable. This toxin is apparently internalized by receptor-mediated endocytosis, probably involving a glycoprotein receptor containing N-acetyl-D-glucosamine. Evidence for toxin binding to lipids was not found. Antibody appeared to detect internalized toxin, and high concentrations of sugars inhibited cytotoxicity; these results along with evidence from a recent ultrastructural study suggest that this toxin may form pores in the cell membrane.