Ultrastructure of the midgut in Ornithodoros papillipes (Acarina, Argasidae) nymphs in the blood assimilation period

Three types of cells (reserve, digestive and secretory) differing in their ultrastructural characters were found to exist in the epithelium of the midgut of nymphs of O. papillipes during the blood assimilation. Reserve and secretory cells are dominant at the first stage of digestion while digestive cells are most abundant at the second one. Ultrafine structure of secretory and digestive cells points to the labile relationship between these types of cells. The same digestive cells assimilate blood both by means of phagocytosis of formed elements and by pinocytosis of its liquid components. The identity of ultrastructural peculiarities of endocytosis and intracellular blood digestion in ixodid and argasid ticks is shown.     

Combined action of anti-arrhythmia agents

A significant potentiation of antiarrhythmic effect was observed in 121 dogs with arrhythmias 24 and 48 hours after the coronary artery ligation when the following drugs were combined: N-propylajmaline bromide (1A class) and trimecaine (1B class), quinidine (1A class) and trimecaine, N-propylajmaline bromide and anaprilin (2 class). The potentiation is attributed to the different molecular mechanisms of action of the drugs.     

Reconstitution of gloeobacter rhodopsin with echinenone: role of the 4-keto group

In previous work, we reconstituted salinixanthin, the C(40)-carotenoid acyl glycoside that serves as a light-harvesting antenna to the light-driven proton pump xanthorhodopsin, into a different protein, gloeobacter rhodopsin expressed in Escherichia coli, and demonstrated that it transfers energy to the retinal chromophore [Imasheva, E. S., et al. (2009) Biochemistry 48, 10948]. The key to binding of salinixanthin was the accommodation of its ring near the retinal β-ionone ring. Here we examine two questions. Do any of the native Gloeobacter carotenoids bind to gloeobacter rhodopsin, and does the 4-keto group of the ring play a role in binding? There is no salinixanthin in Gloeobacter violaceous, but a simpler carotenoid, echinenone, also with a 4-keto group but lacking the acyl glycoside, is present in addition to β-carotene and oscillol. We show that β-carotene does not bind to gloeobacter rhodopsin, but its 4-keto derivative, echinenone, does and functions as a light-harvesting antenna. This indicates that the 4-keto group is critical for carotenoid binding. Further evidence of this is the fact that salinixanthol, an analogue of salinixanthin in which the 4-keto group is reduced to hydroxyl, does not bind and is not engaged in energy transfer. According to the crystal structure of xanthorhodopsin, the ring of salinixanthin in the binding site is turned out of the plane of the polyene conjugated chain. A similar conformation is expected for echinenone in the gloeobacter rhodopsin. We suggest that the 4-keto group in salinixanthin and echinenone allows for the twisted conformation of the ring around the C6-C7 bond and probably is engaged in an interaction that locks the carotenoid in the binding site.     

Regulation of Aggregatibacter (Actinobacillus) actinomycetemcomitans leukotoxin secretion by iron

The gram-negative oral and systemic pathogen Aggregatibacter (Actinobacillus) actinomycetemcomitans produces a leukotoxin (LtxA) that is a member of the RTX (repeats in toxin) family of secreted bacterial toxins. We have recently shown that LtxA has the ability to lyse erythrocytes, which results in a beta-hemolytic phenotype on Columbia blood agar. To determine if LtxA is regulated by iron, we examined beta-hemolysis under iron-rich and iron-limiting conditions. Beta-hemolysis was suppressed in the presence of FeCl3. In contrast, strong beta-hemolysis occurred in the presence of the iron chelator deferoxamine. We found that secretion of LtxA was completely inhibited by free iron, but expression of ltxA was not regulated by iron. Free chromium, cobalt, and magnesium did not affect LtxA secretion. Other LtxA-associated genes were not regulated by iron. Thus, iron appears to play an important role in the regulation of LtxA secretion in A. actinomycetemcomitans in a manner independent of gene regulation.     

Breaking the Carboxyl Rule: LYSINE 96 FACILITATES REPROTONATION OF THE SCHIFF BASE IN THE PHOTOCYCLE OF A RETINAL PROTEIN FROM EXIGUOBACTERIUM SIBIRICUM*?

A lysine instead of the usual carboxyl group is in place of the internal proton donor to the retinal Schiff base in the light-driven proton pump of Exiguobacterium sibiricum (ESR). The involvement of this lysine in proton transfer is indicated by the finding that its substitution with alanine or other residues slows reprotonation of the Schiff base (decay of the M intermediate) by more than 2 orders of magnitude. In these mutants, the rate constant of the M decay linearly decreases with a decrease in proton concentration, as expected if reprotonation is limited by the uptake of a proton from the bulk. In wild type ESR, M decay is biphasic, and the rate constants are nearly pH-independent between pH 6 and 9. Proton uptake occurs after M formation but before M decay, which is especially evident in D₂O and at high pH. Proton uptake is biphasic; the amplitude of the fast phase decreases with a pK_a of 8.5 ± 0.3, which reflects the pK_a of the donor during proton uptake. Similarly, the fraction of the faster component of M decay decreases and the slower one increases, with a pK_a of 8.1 ± 0.2. The data therefore suggest that the reprotonation of the Schiff base in ESR is preceded by transient protonation of an initially unprotonated donor, which is probably the ϵ-amino group of Lys-96 or a water molecule in its vicinity, and it facilitates proton delivery from the bulk to the reaction center of the protein.     

Photoperiod-temperature interaction-a new form of seasonal control of growth and development in insects and in particular a Carabid Beetle, <Emphasis Type="Italic">Amara communis</Emphasis> (Coleoptera: Carabidae)

Amara communis larvae were found to develop significantly faster and to have higher growth rate at short-day (12 h) as compared to long-day (22 h) photoperiods at all used temperatures (16, 18, 20, and 22°C). The coefficient of linear regression of larval development rate on temperature was significantly higher at the short day than at the long day. The thermal developmental thresholds appeared similar at both photoperiods. Body weight of young beetles reared under different photoperiods was almost the same. Thus, photoperiod does not simply accelerate or decelerate insect development, but modifies the thermal reaction norm. At short days, larval development becomes faster and more temperature-dependent, which provides a timely completion of development at the end of summer. The analysis of literature data has allowed us to find the photoperiodic modification of thermal requirements for development in 5 insect orders: Orthoptera, Heteroptera, Coleoptera, Lepidoptera, and Diptera. Modification may result in significant changes in the slope of the regression line, and hence the sum of degree-days, and in the thermal developmental threshold. Consequently, the thermal requirements for development in many insects gradually vary during summer under the effect of changing day-length, which may have adaptive significance. Thus, the photoperiodic modification of thermal reaction norms acts as a specific form of seasonal control of insect development.     

Demography and population models of ticks of the genus Ixodes with long-term life cycles

The most important parameters necessary for the creation of population models for threehost species with long-term life cycles are discussed with an example of ticks Ixodes persulcatus and I. ricinus. In these species, specimens of the same biological age may belong to different age cohorts and their calendar age may differ by several months or even years. Accurate estimation of the calendar age of separate individuals is dofficult; it is based on the extrapolation by its possible biological age and by belonging to the certain age cohort of a natural population. Population models that can predict simultaneous abundance of activated hungry specimens of all the three developmental stages and probability of host-finding in hyngry ticks during questing period possess the prognostic value. Daily mortality of ticks of different developmental stages and phases of each stage (questing, feeding, preparation for molting, and diapause) must also be known. The abundance of questing hungry ticks in the ecosystem is determined by the balance between recruitment of the population with new individuals, their selection by hosts, dying of ticks from starvation, and consumption of ticks by predators. At present, unfortunately, only some of these parameters are known rather sufficiently.     

Study of intrapopulational variability of duration and temperature norms of development of the linden bug Pyrrhocoris apterus (Heteroptera, Pyrrhocoridae)

The existence of significant variability in duration and temperature norms of development between families within insect populations has been shown for the first time. This variability is inferfamily and therefore has genetic ground. Revealed for the first time is the statistically significant positive correlation between the regression coefficient of the development rate for temperature and the temperature threshold for development of eggs and larvae from different families. The greater the slope of the regression line of the development rate for temperature, the higher the temperature threshold value in this particular family. These results demonstrate for the first time the existence of genetic co-variation between the regression coefficient and the temperature threshold within the insect populations. It is suggested that the source of the interpopulational and interspecies changes in the temperature reaction norms of the insect development might be the intrapopulational hereditary variability of the development duration, regression coefficient, and the development threshold, this variability being an object of natural selection. It was shown that in all studied families and populations the values of the linear regression coefficient of development rates for temperature in eggs of the linden bug Pyrrhocoris apterus were markedly and statistically significantly higher, while the temperature threshold values—lower as compared with the corresponding parameters in larvae. These results obviously are in contradiction with the concept of the “isomorphism of development rates” (Jarosik et al., 2002), according to which the development threshold for all life cycle stages of a species should be the same, whereas only slopes of the regression lines of the development rate for temperature can differ. For the first time the absence of genetic covariation has been shown between the temperature norms of development of different life cycle stages of the species—eggs and larvae. This means that the regression coefficient as well as the sum of the degree-days and the development threshold in eggs and larvae are inherited independently and therefore they can be independently changed in evolution in correspondence with specific environmental conditions, under which these life cycle stages take place.     

The role of deformability of endothelial cells in the arterial response to shear tension

Treatment of the femoral artery luminal surface with glutaraldehyde dimere or dithiosuccinimidyl propionate reduced or eliminated flow-induced dilation, the responses to acetylcholine and the ATP being preserved. The findings suggest that the endothelial cells perceive changes in shear stress and that the cell stiffness is a factor subject to the influence of the magnitude of flow-induced arterial dilation.     

Evidence for the rate of the final step in the bacteriorhodopsin photocycle being controlled by the proton release group: R134H mutant

Light absorbed by bacteriorhodopsin (bR) leads to a proton being released at the extracellular surface of the purple membrane. Structural studies as well as studies of mutants of bR indicate that several groups form a pathway for proton transfer from the Schiff base to the extracellular surface. These groups include D85, R82, E204, E194, and water molecules. Other residues may be important in tuning the initial state pK(a) values of these groups and in mediating light-induced changes of the pK(a) values. A potentially important residue is R134: it is located close to E194 and might interact electrostatically to affect the pK(a) of E194 and light-induced proton release. In this study we investigated effects of the substitution of R134 with a histidine on light-induced proton release and on the photocycle transitions associated with proton transfer. By measuring the light-induced absorption changes versus pH, we found that the R134H mutation results in an increase in the pK(a) of the proton release group in both the M (0.6 pK unit) and O (0.7 pK unit) intermediate states. This indicates the importance of R134 in tuning the pK(a) of the group that, at neutral and high pH, releases the proton upon M formation (fast proton release) and that, at low pH, releases the proton simultaneously with O decay (slow proton release). The higher pK(a) of the proton release group found in R134H correlates with the slowing of the rate of the O --> bR transition at low pH and probably is the cause of this slowing. The pH dependence of the fraction of the O intermediate is altered in R134H compared to the WT but is similar to that in the E194D mutant: a very small amount of O is present at neutral pH, but the fraction of O increases greatly upon decreasing the pH. These results provide further support for the hypothesis that the O --> bR transition is controlled by the rate of deprotonation of the proton release group. These data also provide further evidence for the importance of the R134-E194 interaction in modulating proton release from D85 after light has led to its being protonated.