Iodoacetate protects hippocampal neurons against excitotoxic and oxidative injury: involvement of heat-shock proteins and Bcl-2.

Mild metabolic stress may increase resistance of neurons in the brain to subsequent, more severe insults, as demonstrated by the ability of ischemic pre-conditioning and dietary restriction to protect neurons in experimental models of stroke- and age-related neurodegenerative disorders. In the present study we employed iodoacetic acid (IAA), an inhibitor of glyceraldehyde-3-phosphate dehydrogenase, to test the hypothesis that inhibition of glycolysis can protect neurons. Pre-treatment of cultured hippocampal neurons with IAA can protect them against cell death induced by glutamate, iron and trophic factor withdrawal. Surprisingly, protection occurred with concentrations of IAA (2-200 nM) much lower than those required to inhibit glycolysis. Pre-treatment with IAA results in suppression of oxyradical production and stabilization of mitochondrial function in neurons after exposure to oxidative insults. Levels of the stress heat-shock proteins HSP70 and HSP90, and of the anti-apoptotic protein Bcl-2, were increased in neurons exposed to IAA. Our data demonstrate that IAA can stimulate cytoprotective mechanisms within neurons, and suggest the possible use of IAA and related compounds in the prevention and/or treatment of neurodegenerative conditions.     

Isolation and Study of Some Properties of Laccase from the Basidiomycetes Cerrena maxima

A new strain producing extracellular laccase (Cerrena maxima 0275) was found by screening of isolates of Basidiomycetes, and the dynamics of laccase biosynthesis by this strain was studied. The enzyme was purified to homogeneity. The molecular weight of the enzyme is 57 kD, and its pI is 3.5. The activity is constant at pH values in the range 3.0-5.0. The temperature optimum for activity is 50°C. The thermal stability of the laccase was studied. The catalytic and Michaelis constants for catechol, hydroquinone, sinapinic acid, and K₄ Fe(CN)₆ were determined. The standard redox potential of type 1 copper in the enzyme is 750 ± 5 mV. Thus, the investigated laccase is a high redox potential laccase.     

Effects of K+ Channel Blockers and Nitric Oxide on the Electrical and Contractile Activities of Smooth Muscles of the Rabbit Main Pulmonary Artery

Using a sucrose-bridge technique, we studied electrical and mechanical responses of smooth muscle ring strips of the rabbit main pulmonary artery to applications of blockers of voltage-operated (including Ca²⁺-dependent) K⁺ channels, tetraethylammonium (TEA) and 4-aminopyridine (4-AP), as well to application of nitric oxide (NO); nitroglycerin (NG) was used as a donor of the latter. All experiments were carried out under conditions of blockade of the adreno- and cholinoreceptors in the preparation. Both TEA and 4-AP evoked dose-dependent effects: depolarization of smooth muscle cells (SMC) and their contraction. Simultaneous addition of TEA and 4-AP to the normal superfusate (Krebs solution) resulted in intensification of depolarization and initiated generation of action potentials (AP); contractions became rather intensive and possessed a tetanic pattern. Addition of NG to TEA- and 4-AP-containing Krebs solution effectively suppressed AP generation and contractions, whereas the depolarization level underwent only mild modifications. These findings show that Ca²⁺-dependent high-conductance K⁺ channels (K_Ca channels) and 4-AP-sensitive voltage-operated K⁺ channels (K_V channels) are involved in the formation of the resting membrane potential (RMP) in SMC of the rabbit main pulmonary artery. The impact of the K_Ca channels is greater than that of the K_V channels. We suppose that the effects of NO on SMC are related to inhibition of the activity of high-threshold voltage-operated L-type Ca²⁺ channels and, probably, to lowering of the sensitivity of the contractile SMC apparatus to Ca²⁺.     

Biogenesis of Respiratory Complex I

Proteins specifically involved in the biogenesis of respiratory complex I in eukaryotes have been characterized. The complex I intermediate associated proteins CIA30 and CIA84 are tightly bound to an assembly intermediate of the membrane arm. Like chaperones, they are involved in multiple rounds of membrane arm assembly without being part of the mature structure. Two biosynthetic subunits of eukaryotic complex I have been characterized. The acyl carrier subunit is needed for proper assembly of the peripheral arm as well as the membrane arm of complex I. It may interact with enzymes of a mitochondrial fatty acid synthetase. The 39/40-kDa subunit appears to be an isomerase with a tightly bound NADPH. It is related to a protein family of reductases/isomerases. Both subunits have been discussed to be involved in the synthesis of a postulated, novel, high-potential redox group.     

Individuation of monoclonal anti-HPV16 E7 antibody linear peptide epitope by computational biology

We applied computational biology to identify the linear amino acid sequence recognized by a mouse monoclonal antibody raised against the full length HPV16 E7 oncoprotein. Computer-assisted search for the epitopic peptide used two parameters: the capability of E7 peptides to bind to MHC class II molecules, and the similarity level of the oncoprotein sequence to the mouse proteome. We report that anti-E7 mAb recognized the peptide having both high binding potential to MHC II molecules and low level of molecular mimicry to mouse proteome. Peptide ability to bind to MHC II molecules appears a necessary but not sufficient condition to determine peptide immunodominance, by needing to be supported by a low degree of peptide similarity to the host’s proteome.     

Growth and Photosynthetic Characteristics in Pearl Millet under Water Stress and Different Potassium Supply

Influence of supra-optimal concentrations of K on growth, water relations, and photosynthetic capacity in pearl millet under severe water deficit conditions was assessed in a glasshouse. Nineteen-days-old plants of two lines, ICMV-94133 and WCA-78, of Pennisetum glaucum (L.) R.Br. were subjected for 30 d to 235.0, 352.5, and 470.0 mg(K) kg^–1(soil) and two water regimes (100 and 30 % field capacity). Increasing K supply did not alleviate the effect of water deficit on the growth of two lines of pearl millet since additional amount of K in the growth medium had no effect on shoot dry mass, relative growth rate, plant leaf area, net assimilation rate, or leaf area ratio, although there was significant effect of drought stress on these variables. Soil moisture had a significant effect on net photosynthetic rate (P _N), transpiration rate, stomatal conductance, and water use efficiency of both pearl millet lines, but there was no significant effect of varying K supply on these variables. In WCA-78 an ameliorative effect of increasing supply of K on P _N was observed under water deficit. Chlorophyll (Chl) a and b contents increased significantly in both lines with increase in K supply under well watered conditions, but under water deficit they increased only in ICMV-94133. Chl a/b ratios were reduced significantly in WCA-78 with increasing K supply under both watering regimes, but by contrast, in ICMV-94133 this variable was decreased only under water stress. Leaf water potential and osmotic potential of both lines decreased significantly with the imposition of drought. Leaf pressure potential in both lines increased with increase in K supply under water stress. Contents of total free amino acids in the leaves of both pearl millet lines increased significantly with increase in K supply under water stress. Potassium supply had no effect on leaf soluble sugars or soluble proteins. Considerable osmotic adjustment occurred in pearl millet plants experiencing water deficit under high K supply.     

Influence of ionic strength on sodium-calcium exchange of two temperate climate soils

Salt-affected soils have been studied extensively with respect to their Na–Ca exchange properties. These studies have focused on soil environments of the arid West. However, because of irrigation and oil well brine discharges in the temperate region of the U.S. there is need to understand sodicity behavior of such soils. In this study, two Kentucky soils (Pembroke and Uniontown) at the 0–10 cm depth were studied to evaluate the influence of ionic strength (I) and sodium adsorption ratio (SAR) on cation selectivity coefficients. The data showed that both soils exhibit at least two classes of exchange sites and in general the apparent affinity for Na⁺ increased when solution ionic strength increased. Furthermore, both soils under all three ionic strengths tested showed greater affinity for Na⁺ than the average agricultural saline soil of the arid West. The data suggested the need for establishing critical salt dispersion thresholds for temperate climate soils and developing effective brine management approaches.     

Photosynthetic Response to Soil Water Contents of an Annual Pioneer C4 Grass (Agriophyllum squarrosum) in Hunshandak Sandland,China

Net photosynthetic rate (P _N), transpiration rate (E), stomatal conductance (g _s), and leaf water potential (Ψ_l) of an annual pioneer C₄ grass (Agriophyllum squarrosum) were compared under different simulated precipitation events in a field of Hunshandak Sandland, China. The increase of soil water content (SWC) had significant effect on these physiological traits (p<0.001). In the vegetative stage, the values of P _N, E, and g _s went up sharply when SWC increased at the beginning, while they went down with continuous increase of SWC. P _N, E, and g _s increased 1.4, 1.7, and 1.7 fold, respectively, with SWC range from 6.7 to 11.6 %. In the reproductive stage, similar trends were found, except for the climate with a higher SWC. This indicated that A. squarrosum was very sensitive to the small increment of SWC which might have a large photosynthetic potential. Ψ_l increased by about 8 % as the SWC changed from 6.7 to 8.8 %, and then maintained a steady level when the SWC was higher than 8.8 %, while the values of P _N, E, and g _s kept increasing even after this SWC. This might indicate that the adjustment of Ψ_l response to the changes of SWC lagged that of the photosynthetic parameters. This revised version was published online in August 2006 with corrections to the Cover Date.     

Redox potentials of the oriented film of the wild-type, the E194Q-, E204Q- and D96N-mutated bacteriorhodopsins

The redox potentials of the oriented films of the wild-type, the E194Q-, E204Q- and D96N-mutated bacteriorhodopsins (bR), prepared by adsorbing purple membrane (PM) sheets or its mutant on a Pt electrode, have been examined. The redox potentials (V) of the wild-type bR were −470 mV for the 13-cis configuration of the retinal Shiff base in bR and −757 mV for the all-trans configuration in H₂O, and −433 mV for the 13-cis configuration and −742 mV for the all-trans configuration in D₂O. The solvent isotope effect (ΔV=V(D₂O)−V(H₂O)), which shifts the redox potential to a higher value, originates from the cooperative rearrangements of the extensively hydrogen-bonded water molecules around the protonated CN part in the retinal Schiff base. The redox potential of bR was much higher for the 13-cis configuration than that for the all-trans configuration. The redox potentials for the E194Q mutant in the extracellular region were −507 mV for the 13-cis configuration and −788 mV for the all-trans configuration; and for the E204Q mutant they were −491 mV for the 13-cis configuration and −769 mV for the all-trans configuration. Replacement of the Glu¹⁹⁴ or Glu²⁰⁴ residues by Gln weakened the electron withdrawing interaction to the protonated CN bond in the retinal Schiff base. The E204 residue is less linked with the hydrogen-bonded network of the proton release pathway compared with E194. The redox potentials of the D96N mutant in the cytoplasmic region were −471 mV for the 13-cis configuration and −760 mV for the all-trans configuration which were virtually the same as those of the wild-type bR, indicating that the D to N point mutation of the 96 residue had no influence on the interaction between the D96 residue and the CN part in the Schiff base under the light-adapted condition. The results suggest that the redox potential of bR is closely correlated to the hydrogen-bonded network spanning from the retinal Schiff base to the extracellular surface of bR in the proton transfer pathway.     

Sodium—A Functional Plant Nutrient

Plant scientists usually classify plant mineral nutrients based on the concept of “essentiality” defined by Arnon and Stout as those elements necessary to complete the life cycle of a plant. Certain other elements such as Na have a ubiquitous presence in soils and waters and are widely taken up and utilized by plants, but are not considered as plant nutrients because they do not meet the strict definition of “essentiality.” Sodium has a very specific function in the concentration of carbon dioxide in a limited number of C₄ plants and thus is essential to these plants, but this in itself is insufficient to generalize that Na is essential for higher plants. The unique set of roles that Na can play in plant metabolism suggests that the basic concept of what comprises a plant nutrient should be reexamined. We contend that the class of plant mineral nutrients should be comprised not only of those elements necessary for completing the life cycle, but also those elements which promote maximal biomass yield and/or which reduce the requirement (critical level) of an essential element. We suggest that nutrients functioning in this latter manner should be termed “functional nutrients.” Thus plant mineral nutrients would be comprised of two major groups, “essential nutrients” and “functional nutrients.” We present an array of evidence and arguments to support the classification of Na as a “functional nutrient,” including its requirement for maximal biomass growth for many plants and its demonstrated ability to replace K in a number of ways, such as being an osmoticium for cell enlargement and as an accompanying cation for long-distance transport. Although in this paper we have only attempted to make the case for Na being a “functional nutrient,” other elements such as Si and Se may also confirm to the proposed category of “functional nutrients.”