Tuning of electron delocalization in polynuclear mixed-valence clusters by super-exchange and double exchange

 Values for the exchange-coupling constant J and the double-exchange parameter B have been estimated for dimeric and hexameric mixed-valence iron clusters. For sulfur-bridged species the range of J values is 300–450 cm^–1, and B values vary between 320 and 400 cm^–1. For an OH-bridged diiron cluster B is as large as 1300 cm^–1. Received and accepted: 23 January 1996     

Inhibition of protein synthesis in a polyribosome-dependent cell-free system by a specific ribonuclease prepared from the follicles of two different stages of development of the silkmothAntherea pernyi

Summary Crude, cell-free protein-synthesizing systems were prepared from follicles of two different stages of development in the ovariole of the silkmothAntherea pernyi. The efficiency of the translation of natural and synthetic mRNAs in these systems was compared with that in a cell-free wheat germ system. A postmitochondrial extract (S-30) from the follicles almost completely inhibited protein synthesis in a polyribosome-dependent, cell-free systems. A specific ribonuclease, obtained from the post mitochondrial extract by ammonium sulphate precipitation, heat denaturation and DEAE-cellulose chromatography, inhibited polyribosome-dependent protein synthesis. The effect of this specific ribonuclease on the structural integrity of radioactive RNAs and ribosomal subunits, which were isolated from Ehrlich ascites tumor cells, was also studied.     

Induction of dopa (3,4-dihydroxyphenylalanine) decarboxylase in blowfly integument by ecdysone. A demonstration of synthesis of the enzyme de novo.

The activity of the enzyme dopa (3,4-dihydroxyphenylalanine) decarboxylase, present in the epidermis cells of blowfly larvae, increases during the late third instar under the influence of the steroid hormone, ecdysone. By using the double-labelling technique and immune precipitation with univalent antibody to dopa decarboxylase, we demonstrated that the increase in enzyme activity was due to a stimulation of synthesis of enzyme molecules de novo. In this respect, the action of ecdysone is similar to the action of other steroid hormones.     

Dual factor delivery of CXCL12 and Exendin‐4 for improved survival and function of encapsulated beta cells under hypoxic conditions

A bioartifical pancreas (BAP) remains a promising approach for treating insulin‐dependent diabetes. Several obstacles to the clinical implementation of a BAP remain, including hypoxia following implantation. Within native pancreatic islets, CXCL12 and glucagon‐like peptide‐1 (GLP‐1) act in a paracrine fashion to promote the survival, function, and proliferation of β‐cells. This work sought to investigate if the presentation of CXCL12 and delivery of a GLP‐1 receptor analog, Exendin‐4 (Ex‐4), alone and in combination, conferred pro‐survival and insulinotropic effects on an encapsulated β‐cell line, βTC‐tet, cultured under hypoxic conditions of 7.6 mmHg O₂. Our findings indicate that presentation of CXCL12 in the encapsulation matrix completely abrogated apoptosis under hypoxic conditions. Delivery of Ex‐4 increased insulin secretion rate under both normoxic and hypoxic conditions, and additionally reduced apoptosis under hypoxic conditions. Furthermore, presentation of CXCL12 combined with Ex‐4 delivery significantly increased insulin secretion rate under hypoxic conditions compared to delivery of Ex‐4 alone. These findings demonstrate that the presentation of CXCL12 combined with the delivery of Ex‐4 may constitute a promising strategy for supporting β‐cell function and survival following transplantation. Biotechnol. Bioeng. 2013; 110: 2292–2300. © 2013 Wiley Periodicals, Inc.     

Chemical stimuli from corn plants affect host selection and oviposition behavior of Sesamia nonagrioides (Lepidoptera: Noctuidae)

The role of chemical stimuli in host selection and oviposition of Sesamia nonagrioides (Lef) was studied in the laboratory using eight corn hybrids. Female oviposition preference was evaluated on plants of the eight hybrids, their extracts in pentane and methanol, and volatiles collected by steam distillation in ether. Results from two-choice bioassays indicate various degrees of female preference to the hybrids. Four hybrids received more eggs than control plants, whereas the remainder received fewer eggs. Relatively similar results were obtained when filter paper sticks baited with pentane and steam distillation extracts were evaluated. Methanol extracts from all eight hybrids received fewer eggs than the methanol controls. Results showed that pentane and steam distillation extracts contain chemicals that elicit female oviposition response, while methanol extracts may contain chemicals that deter or repel females to oviposition.     

Interaction of Al(III) with the peptides AspAsp and AspAspAsp

The interactions of Al(III) with the dipeptide AspAsp and the tripeptide AspAspAsp in aqueous solutions were studied by pH-potentiometry and multinuclear 1H- and 13C- nuclear magnetic resonance (NMR) spectroscopy. Their numerous negatively charged COO(-) functions allow these ligands to bind Al(III) even in weakly acidic solutions. Various mononuclear 1:1 complexes are formed in different protonation states. 13C-NMR spectroscopy unambiguously proved participation of the COO(-) functions in a monodentate or chelating mode in Al(III) binding, however, the terminal-NH(2) group seems to be excluded from the coordination. Depending on the metal ion to ligand ratio precipitation occurs at pH approximately 5 to 6. This indicates that the COO(-) groups at the low level of preorganization in such small peptides are not sufficient to keep the Al(III) ion in solution and to prevent the precipitation of Al(OH)(3) at physiological pH. To achieve this, a more specific arrangement of the side-chain donors seems necessary.     

Asymmetric Mating Interference between Two Related Mosquito Species: Aedes (Stegomyia) albopictus and Aedes (Stegomyia) cretinus

Aedes (Stegomyia) albopictus (Skuse) and Aedes (Stegomyia) cretinus Edwards are closely related mosquito species with common morphological features and bio-ecological similarities. Recent mosquito surveillance in Athens, Greece, showed that they are sympatric mosquito species, with Ae. Albopictus developing quite higher population densities than Ae. Cretinus. The potential of mating interference between these species was investigated by reciprocal and homologous mating experiments in cages under laboratory conditions. In non-choice interspecific crosses (groups of males and females) females of both species produced sterile eggs. Insemination rate was 58% for Ae. Cretinus females and only 1% for Ae. Albopictus females. Aedes albopictus males were sexually aggressive and inseminated Ae. Cretinus females (31%) in choice experiments, where males of one species had access to mate with females of both species. Whereas, interspecific mating of Ae. Albopictus females with Ae. Cretinus males in the co-occurrence of Ae. Cretinus females was weaker (4%). Aedes cretinus females from non-choice crossing with Ae. Albopictus or Ae. Cretinus males were paired individually with conspecific males. The percentage of fertile Ae. Cretinus females was 17.5% when had encaged before with Ae. Albopictus males, compared to 100% when Ae. Cretinus females were encaged with conspecific males only. Probable ecological consequences of asymmetric mating between these ecologically homologous species in nature are discussed.     

Bombesin and neurotensin exert antiproliferative effects on oval cells and augment the regenerative response of the cholestatic rat liver

The regenerative capacity of the cholestatic liver is significantly attenuated. Oval cells are hepatic stem cells involved in liver's regeneration following diverse types of injury. The present study investigated the effect of the neuropeptides bombesin (BBS) and neurotensin (NT) on oval cell proliferation as well as on hepatocyte and cholangiocyte proliferation and apoptosis in the cholestatic rat liver. Seventy male Wistar rats were randomly divided into five groups: controls, sham operated, bile duct ligated (BDL), BDL + BBS (30 μg/kg/d), BDL + NT (300 μg/kg/d). Ten days later, alpha-fetoprotein (AFP) mRNA (in situ hybridization), cytokeratin-19 and Ki67 antigen expression (immunohistochemistry) and apoptosis (TUNEL) were evaluated on liver tissue samples. Cells with morphologic features of oval cells that were cytokeratin-19(+) and AFP mRNA(+) were scored in morphometric analysis and their proliferation was recorded. In addition, the proliferation and apoptotic rates of hepatocytes and cholangiocytes were determined. Alanine aminotransferase (ALT) levels and hepatic oxidative stress (lipid peroxidation and glutathione redox state) were also estimated. The neuropeptides BBS and NT significantly reduced ALT levels and hepatic oxidative stress. Both agents exerted similar and cell type-specific effects on oval cells, hepatocytes and cholangiocytes: (a) oval cell proliferation and accumulation in the cholestatic liver was attenuated, (b) hepatocyte proliferation was increased along with a decreased rate of their apoptosis and (c) cholangiocyte proliferation was attenuated and their apoptosis was increased. These observations might be of potential value in patients with extrahepatic cholestasis.     

Mechanisms of programmed cell death during oogenesis in <Emphasis Type="Italic">Drosophila virilis</Emphasis>

We describe the features of programmed cell death occurring in the egg chambers of Drosophila virilis during mid-oogenesis and late oogenesis. During mid-oogenesis, the spontaneously degenerating egg chambers exhibit typical characteristics of apoptotic cell death. As revealed by propidium iodide, rhodamine-conjugated phalloidin staining, and the TUNEL assay, respectively, the nurse cells contain condensed chromatin, altered actin cytoskeleton, and fragmented DNA. In vitro caspase activity assays and immunostaining procedures demonstrate that the atretic egg chambers possess high levels of caspase activity. Features of autophagic cell death are also observed during D. virilis mid-oogenesis, as shown by monodansylcadaverine staining, together with an ultrastructural examination by transmission electron microscopy. During the late stages of oogenesis in D. virilis, once again, the two mechanisms, viz., nurse cell cluster apoptosis and autophagy, operate together, manifesting features of cell death similar to those detailed above. Moreover, an altered form of cytochrome c seems to be released from the mitochondria in the nurse cells proximal to the oocyte. We propose that apoptosis and autophagy function synergistically during oogenesis in D. virilis in order to achieve a more efficient elimination of the degenerated nurse cells and abnormal egg chambers. The present study was co-financed within Op. Education by the European Social Fund and by National Resources via a grant (HRAKLEITOS 70/3/7164) to Professor L.H. Margaritis.