Thermodynamics of GTP and GDP Binding to Bacterial Initiation Factor 2 Suggests Two Types of Structural Transitions

During initiation of messenger RNA translation in bacteria, the GTPase initiation factor (IF) 2 plays major roles in the assembly of the preinitiation 30S complex and its docking to the 50S ribosomal subunit leading to the 70S initiation complex, ready to form the first peptide bond in a nascent protein. Rapid and accurate initiation of bacterial protein synthesis is driven by conformational changes in IF2, induced by GDP-GTP exchange and GTP hydrolysis. We have used isothermal titration calorimetry and linear extrapolation to characterize the thermodynamics of the binding of GDP and GTP to free IF2 in the temperature interval 4-37 °C. IF2 binds with about 20-fold and 2-fold higher affinity for GDP than for GTP at 4 and 37 °C, respectively. The binding of IF2 to both GTP and GDP is characterized by a large heat capacity change (− 868 ± 25 and − 577 ± 23 cal mol^− 1 K^− 1, respectively), associated with compensatory changes in binding entropy and enthalpy. From our data, we propose that GTP binding to IF2 leads to protection of hydrophobic amino acid residues from solvent by the locking of switch I and switch II loops to the γ-phosphate of GTP, as in the case of elongation factor G. From the large heat capacity change (also upon GDP binding) not seen in the case of elongation factor G, we propose the existence of yet another type of conformational change in IF2, which is induced by GDP and GTP alike. Also, this transition is likely to protect hydrophobic groups from solvent, and its functional relevance is discussed.     

Differential analysis of major natural cytokinins by enzyme immunoassay

An immunochemical method for quantitative differential analysis of major types of natural cytokinins in plant tissues subjected to minimal treatment, without purification or chemical modification of hormones, is proposed. This method is recommended for use in biology, medicine, and agriculture for determination of low-molecular-weight compounds having similar chemical structures but various biological activities.     

Electrical properties of hornet silk: temperature dependence

Hornet silk is a polymer of amino acids. One of the known properties of polymers is their electrical activity. The present study describes the results of electrical measurements carried out vertically on the silk cap of pupae of the Oriental hornet Vespa orientalis (Hymenoptera, Vespinae). The measurements undertaken were the temperature-dependent electric current, voltage and resistance, all measured within the range of biological temperatures, as well as the capacitance. The temperature-dependent spontaneous current attained values up to 327 nano Amperes (nA) while the maximal voltage reached 347 millivolt (mV). The electrical resistance was low and steady (1-20 mu omega) at temperatures ranging between 19-32 degrees C, but at lower or higher temperature it increased fairly sharply by about three orders of magnitude. The electrical capacitance, computed according to the discharge curve (decay curve) amounted to 0.4 microFarad (microF). The paper also discusses the role of the pupal silk as producer of a 'clean room' while the cuticle is being laid down by the pupae after undergoing metamorphosis, as well as the significance of the measured electrical parameters vis-à-vis the developing pupae.     

Boundary potentials of lipid membranes in the presence of 1-anilino-8-naphthalene sulfonate ions

Boundary and zeta potentials induced by ANS adsorption in dioleoyl lecithin membranes were measured using three methods, namely: inner membrane field compensation, measurements of carrier-mediated membrane conductance and microelectrophoresis. The changes of boundary potentials due to ANS adsorption recorded by the first two methods were the same and did not depend on the ionic strength of aqueous solutions. On the contrary, the values of zeta potentials were smaller as compared with the boundary potentials, and depended on the ionic strength. The results obtained were described satisfactorily by means of combination of Henry, Gouy-Chapman and Boltzmann equations, when ANS ions were assumed to adsorb at a plane shifted towards the hydrophobic region of the membrane.     

Regulation of ion transport across the pollen tube plasmalemma by hydrogen peroxide

The polar growth of the pollen tube is a key stage in the life cycle of seed plants, which is critical for successful sexual reproduction. One of the most important components of this process is ion transport across the cell membrane coordinated in time and space. Different classes of signal molecules, including reactive oxygen species, as has been found recently, participate in regulation of ion transmembrane transport. In this study, based on the model system of subprotoplasts isolated from pollen tubes, we showed that hydrogen peroxide can regulate two targets located on the plasma membrane: nifedipine-sensitive Ca²⁺ channels and ion transport, both of which control the membrane potential. The interaction of hydrogen peroxide with these targets resulted in an increase in an intracellular Ca²⁺ concentration and hyperpolarization of the plasma membrane. Faster regeneration of the cell wall was a consequence of elevation of the Ca²⁺ intracellular concentration.     

Simplest Kinetic Schemes for Biochemical Oscillators

The topological structure of the simplest critical fragments in biochemical systems has been characterized. The conditions are considered where the critical fragments induce oscillations of the concentrations of the system participants. To illustrate, three biochemical systems (transport of ions through a membrane, protein phosphorylation, and two-substrate reaction) are discussed. The kinetic schemes of these systems contain one of the discovered critical fragments. Relaxation oscillations of the concentrations of the system participants were demonstrated using the numerical integration method.     

Communication by electrical means in social insects

Social insects, belonging to the order Hymenoptera, maintain a fixed, optimal temperature in their nest. Thus, in social wasps and hornets, the optimal nest temperature is 29 degrees C, despite the fact that they are distributed in regions of varying climates both in the northern and southern hemispheres of the globe. Since hornets and bees are relatively small insects, determination of their own body temperature as well as that of their nest and the brood was made via thermometers or by the use of infrared (IR) rays. It has been suggested that thermoregulation in social insect colonies is effected primarily by the adult insects via muscle activation, that is, fluttering of their wings, which can raise both their own and the ambient temperature by many degrees centigrade. However, the larval brood can also contribute to the thermoregulation by acting as heat resources and thereby raising the ambient temperature by 1-2 degrees C. To this end, the adult hornets are endowed with a well-developed musculature and their larvae, too, have muscles that enable them to move about. Not so the hornet pupae which are enclosed in a silk envelope (the cocoon), with a rather thick silk cap spun by the pupating larvae, and have rather undeveloped muscles. In the latter instance, it stands to reason that the pupae benefit from the nest warming achieved primarily by the adult hornets, but how is the information regarding their thermal needs relayed from them to the adults? Previously we showed that the adult hornets are attracted to the pupae by pheromones released by the latter, but such chemical compounds can only convey information of a general nature and we are still left with the question as to how the adult hornet can gauge or ascertain the temperature of a single insulated pupa. The present study provides evidence that the hornet pupa can indeed transmit information regarding its body temperature via electrical means.