EphA-Ephrin-A-mediated beta cell communication regulates insulin secretion from pancreatic islets

In vertebrates, beta cells are aggregated in the form of pancreatic islets. Within these islets, communication between beta cells inhibits basal insulin secretion and enhances glucose-stimulated insulin secretion, thus contributing to glucose homeostasis during fasting and feeding. In the search for the underlying molecular mechanism, we have discovered that beta cells communicate via ephrin-As and EphAs. We provide evidence that ephrin-A5 is required for glucose-stimulated insulin secretion. We further show that EphA-ephrin-A-mediated beta cell communication is bidirectional: EphA forward signaling inhibits insulin secretion, whereas ephrin-A reverse signaling stimulates insulin secretion. EphA forward signaling is downregulated in response to glucose, which indicates that, under basal conditions, beta cells use EphA forward signaling to suppress insulin secretion and that, under stimulatory conditions, they shift to ephrin-A reverse signaling to enhance insulin secretion. Thus, we explain how beta cell communication in pancreatic islets conversely affects basal and glucose-stimulated insulin secretion to improve glucose homeostasis.     

The symptomless leaf infection with grapevine leafroll associated virus 3 in grown in vitro plants as a simple model system for investigation of viral effects on photosynthesis

The photosynthetic changes evaluated by oxygen evolution, chlorophyll fluorescence, photoacoustics, and delayed fluorescence (DF) were studied in leaves of grown in vitro for 8 weeks grapevine plants (Vitis vinifera) infected by grapevine leafroll-associated virus 3 (GLRaV-3). The infected leaves were characterized during the viral infection without visible disease symptoms. The symptomless infection led to a decrease in plant biomass. The non-photochemical fluorescence quenching, qN, declined, whereas the photochemical quenching, qP, and the Chl a/b ratio were not significantly affected. Photoacoustic and oxygen evolution measurements showed that the energy storage and oxygen evolution rate decreased in the infected leaves. Enhanced alternative electron sinks during the symptomless viral infection were also estimated. The changes in fluorescence and DF temperature curves demonstrated an enhanced stability of the thylakoid membranes in the infected leaves. This effect was clearly expressed at high actinic light intensities. The viral infected in vitro grown grapevine plants were used in the present study as a simplified model system that allow to avoid the involvement of different environmental factors that could interfere with the GLRaV infection and the virus-grapevine interactions. Thus, the 'pure' impact of the viral infection on photosynthesis could be investigated.     

Estimation of male and female body segment parameters of the Bulgarian population using a 16-segmental mathematical model

Based on a large-scale anthropometric measurements of 5290 individuals (2435 males and 2855 females) of the Bulgarian population aged between 30 and 40 years, we present 16-segmental 3D geometrical model of the human body of the average Bulgarian male and female and calculate mass, volume, location of the mass center and moments of inertia for all the segments for both genders. This study extends current anthropometrical data pool of Caucasian. Wherever possible, the comparison between our model results and data reported in literature for other Caucasian shows an overall good agreement, thus supporting the validity of the described method.     

Sphingomyelin and ceramide: phosphoethanolamine synthesis in ram spermatozoa plasma membrane

1. The possibility for sphingomyelin and ceramide: phosphoethanolamine synthesis in ram spermatozoa plasma membranes has been established. 2. Ceramide: phosphoethanolamine formation appears to be higher than the synthesis of sphingomyelin. 3. The pH optimum of the phosphatidylethanolamine: ceramide-phosphoethanolamine transferase is about 7.0. An inhibition of its activity was observed in the presence of Ca2+ and Zn2+ ions.     

Deciduous forest communities in the Black Sea coastal Strandzha region: temporal and spatial characteristics of leaf area index and density

The seasonal variation and vertical distribution of leaf area index are important characteristics of forest stands and their structure, not in the least for modelling and assessing biogeochemical and biogeophysical processes. In this paper results are presented from 2 years' measurements with the Li-Cor LAI-2000 Plant Canopy Analyser in the south-eastern part of the Bulgarian Black Sea coast, where Quercus frainetto stands are well represented but so far little studied. Mixed Fagus orientalis and Quercus polycarpa stands were also studied. The Q. frainetto effective LAI-2000 leaf area index values (one-sided) ranged from 1.43 to 3.21 with maximum values in June. Several Q. frainetto and F. orientalis + Q. polycarpa stands in the coastal zone were studied extensively and are shown to follow the seasonal variation at an intensive-measurements site, with an increase in leaf area index by 39.6% and 45.5% in June, respectively, related to the April values. The vertical profile of the canopy in the intensive-measurements site is presented and destructive measurements are compared with the LAI-2000 data. Data show that most of the leaves are located close to the middle of tree height (at around 40% of it). The analysis suggests that the intensive-measurements site is a good representative of the region, and that LAI-2000 measurements can provide sufficiently good information for further mapping of its forest leaf-area characteristics.     

Substrate Specificity of the Highly Alkalophilic Bacterial Proteinase Esperase: Relation to the X-Ray Structure

Esperase is a highly alkalophilic bacterial proteinase produced by Bacillus lentus. The enzyme hydrolyzes peptide bonds comprising the carboxylic groups of hydrophobic as well as hydrophilic residues in the oxidized insulin B chain. Some of these bonds are not attacked by other alkaline microbial proteinases. P1-P4 specificity was determined by a series of peptide nitroanilides. The S1 recognition loop exhibits a preference for Phe. The "cleft" of the smallest subsite S2 prefers Ala and exhibits low affinity for the larger chain of Leu. S3 is more open than the other subsites and can accept a variety of residues. Hydrophobic interactions predominate in the S4-P4 interactions because S4 can accommodate Phe very well. The results characterize Esperase as an endopeptidase with a broader specificity in comparison with other microbial serine proteinases. This is probably owing to a more flexible substrate binding site.