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.     

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.     

Hyperosmotic relaxation lysis of chromaffin granules is caused by interactions between the granular membrane and intragranular vesicles

Bovine chromaffin granules undergo irreversible structural changes during osmotic shrinkage in hypertonic sucrose and salt solutions, such that, on reexposure to isoosmotic conditions they do not regain their original morphology, but undergo lysis ('hyperosmotic relaxation lysis'). Irreversible alterations of granules were induced by hypertonic incubations lasting for as little as 1 min. Fluorescence and EPR membrane labelling experiments showed that hypertonicity did not induce membrane loss for instance by inwardly or outwardly directed pinching off of membrane material. The mean sizes of chromaffin granules as a function of increasing and subsequently decreasing osmotic pressure were measured by photon correlation spectroscopy; there was no significant difference in sizes of hyperosmotically pretreated granules as compared with controls. Freeze-fracture electron micrographs showed the formation of 'twins' and 'triplets' under hypertonic conditions. They also revealed intragranular vesicles of 50-200 nm in diameter in both hypertonically and isotonically suspended granules. 'Twin' and 'triplet' granules were formed by the attachment of intragranular vesicles to the granule membranes. We suggest that hyperosmotic relaxation lysis is caused by the fact that this adhesion partly prevents the granule membrane from reexpanding, thus, leading to its rupture.     

Cardiac troponin I, isolated from bovine heart, contains two adjacent phosphoserines. A first example of phosphoserine determination by derivatization to S-ethylcysteine

Bovine cardiac troponin containing approximately 3 mol P/mol protein could be separated into its subunits without loss of phosphate. Troponin I and troponin T each contain about 1.5 mol P/mol protein. In troponin I two phosphorylated serine residues could be localized in the N-terminal region by conversion of phosphoserine to S-ethylcysteine. They are located in adjacent positions in the following sequence: -Arg-Arg-Ser(P)-Ser(P)-Ala-Asn-Tyr-Tyr-Arg-Ala-Tyr-Ala-Thr-Glu-Pro- His-Ala-Lys. This sequence shows that the first phosphoserine residue in bovine cardiac troponin I occupies a homologous position to phosphoserine-20 of rabbit cardiac troponin I.     

Delta 5-3 beta-hydroxysteroid dehydrogenase, succinate dehydrogenase and glucose-6-phosphate dehydrogenase in the bovine corpus luteum of estrous cycle: a quantitative histochemical study

Genital organs and blood were obtained from dairy cows at a local abattoir. 3 recently ovulated follicles and 20 corpora lutea of estrous cycle (CLC) were used for the quantitative enzyme histochemical demonstration of delta 5-3 beta-hydroxysteroid dehydrogenase (3 beta-OHSDH), succinate dehydrogenase (SDH) and glucose-6-phosphate dehydrogenase (G-6-PDH) activity, employing a computerized microscope photometer. Progesterone was determined in blood serum by radioimmunoassay. Luteal tissue was grouped into several stages of development according to micromorphological criteria. Activities per volume unit of 3 beta-OHSDH and SDH in large luteal cells (LLC), as well as in small luteal cells (SLC), and luteal tissue (LT), relative amounts of the 3 beta-OHSDH-positive tissue fraction (PLCC), and progesterone concentrations in blood serum exhibited a significant pattern corresponding to the morphological development of the endocrine gland. G-6-PDH showed an increase in activity per volume unit during tissue development lasting until the beginning of regressive changes, and as significant in LLC and LT. Activities per volume unit of 3 beta-OHSDH (p less than or equal to 0.001) and SDH (p less than or equal to 0.01) were higher in LLC than in SLC, indicating superior steroidogenic capacities, while G-6-PDH activity was distinctly higher in the latter (p less than or equal to 0.001). Almost all parameters tested were correlated positively. 3 beta-OHSDH and SDH exhibited a significantly positive correlation in LLC (p less than or equal to 0.01) and LT (p less than or equal to 0.001) during periods of measureable progesterone secretion. In SLC this correlation was nonsignificant (p greater than 0.05). G-6-PDH showed a relative poor correlation to 3 beta-OHSDH (LLC, p less than or equal to 0.05; LT, p less than or equal to 0.01) and SDH (LT, p less than or equal to 0.05). Enzyme activities in LLC as well as in SLC were generally positively correlated (p less than or equal to 0.001). All enzymes tested exhibited a significantly positive correlation with progesterone concentrations in blood serum. This was significant for SDH only during measurable progesterone secretion, and less marked for G-6-PDH.     

Epithelial-mesenchymal interactions: effects of a dental biomatrix on odontoblasts

The functional differentiation of odontoblasts requires specific interactions between these cells and the extracellular matrix. To further analyze these phenomena we studied the effects of a "dental papillae biomatrix" on isolated dental papillae cultured in vitro. The dental papillae biomatrix was extracted from EDTA-dissociated day-18 mouse dental papillae by homogenization, NaCl and enzymatic treatments, and deposited on Millipore filters. This biomatrix was studied by means of transmission electron microscopy and indirect immunofluorescence: it contained collagen fibrils, type IV collagen, fibronectin and laminin; cellular residues were also observed. The dental papillae were isolated by trypsin treatment of homologous tooth germs and cultured on uncoated (control) and coated filters. As shown by histological and cytological data, odontoblast-like cells never differentiated in control cultures. In presence of biomatrix and serum, polarized functional cells were observed. The functional state of these cells was enhanced by the addition of ascorbic acid to the culture media. Study of the incorporation of 3H-proline in cultured dental papillae and in macromolecules secreted into the culture media corroborated the morphological findings.     

Dihydropyridine calcium antagonists depress the amplitude of the plasma melatonin cycle in baboons

An investigation into the effects of verapamil and some dihydropyridine derivatives on plasma melatonin levels was undertaken in baboons. In a number of separate experiments, groups of young male chacma baboons (mean body weight 13 kg) received intraperitoneal injections of the drugs, under ketamine anaesthesia, roughly 30 minutes prior to the following time points: 1200, 1800, 0000, 0200, 0600 and 1200 h. Lights went off at 1800 h and came on at 0600 h. The drugs used, and their respective dosages (expressed per kg body mass), were verapamil up to 4 mg/kg, nifedipine at 0.2 mg/kg, nitrendipine at 0.5 mg/kg and nisoldipine at 0.1 mg/kg. Blood samples, taken at the said time points, were assayed for melatonin. The nighttime peak of the plasma melatonin cycle was significantly depressed by all three dihydropyridine calcium antagonists (up to 40%), while verapamil, even at the relatively high total dose of 24 mg/kg per day, had no significant effect on the circulating plasma melatonin levels.     

Flavocytochromes c: transient kinetics of photoreduction by flavin analogues

Kinetics of reduction of phototrophic bacterial flavocytochromes c by exogenous flavin semiquinones and fully reduced flavins generated by laser flash photolysis have been studied. The mechanisms of reduction of Chromatium and Chlorobium flavocytochromes c are more similar to one another than previously thought. Neither protein is very reactive with neutral flavin semiquinones (k less than 10(7) M-1 s-1), and the reactions with fully reduced flavins are slower than expected on the basis of comparison with other electron-transfer proteins of similar redox potentials. Deazaflavin radical is reactive with the flavocytochromes c by virtue of its low redox potential, but this reaction is also slower than expected on the basis of comparison with other electron-transfer proteins. These experiments indicate that the active site for reduction of flavocytochrome c is relatively buried and probably inaccessible to solvent. Fully reduced FMN does not show an ionic strength effect in its reaction with flavocytochrome c, which demonstrates that the active site is uncharged. Sulfite, which forms an adduct with protein-bound FAD, partially blocks heme reduction. This shows that heme is reduced via the FAD. The rate constant for intramolecular electron transfer between FAD and heme must be on the order of 10(4) s-1 or larger.