The effects of palladium coordination complex speciation and concentration upon the ubiquitous bacterial species Pseudomonas aeruginosa

The toxicity of three different palladium (Pd) species to Pseudomonas aeruginosa, an environmentally ubiquitous bacterial species, is reported. Palladium was added to chemically-defined minimal media as three complex ion salts, namely sodium tetrachloropalladate (Na₂[PdCl₄]), tetraamminepalladium(II) chloride ([Pd(NH₃)₄]Cl₂), and potassium hexachloropalladate(IV) (K₂[PdCl₆]), inoculated with log-phase cultures and incubated for 24 h at 25 °C. Toxicity was tested for Pd concentrations ranging from 6.55 μg/L (0.06 μM Pd) to 250 μg/L (2.33 μM Pd). Minimum inhibitory concentrations (MICs) were determined and growth tracked via optical absorption at 600 nm. Viability and minimum bactericidal concentrations (MBCs) were measured in parallel with dilution, plating and colony forming unit (CFU) counting. MICs for all forms of Pd were 62.5 μg Pd/L, approximately 1000 times lower than previously reported values. The MBCs for PdCl₄^2- and Pd(NH₃)₄²⁺ were 62.5 μg Pd/L and 125 μg Pd/L for PdCl₆^2-. Pd(NH₃)₄²⁺ and PdCl₆^2- culture viability at 7.8-31.3 μg Pd/L was not different from controls. However, PdCl₄^2- culture viability was different from the other additives, with decreasing viability at sub-MBC concentrations down to 6.55 μg Pd/L. To understand the possible effect of speciation upon toxicity, the equilibrium speciation of Pd was modeled for all solutions using PHREEQC and found to be dominated by Pd(NH₃)₃Cl⁺ (65.6 % of total Pd) and Pd(NH₃)₄²⁺ (34.2 % total Pd). The juxtaposition of the equilibrium calculations and the toxicity results indicates that the kinetics of ligand exchange between the palladium complexes and the growth medium could influence bacterial response.

Stabilization of active-site loops in NH3-dependent NAD+ synthetase from Bacillus subtilis

The NH(3)-dependent NAD(+) synthetase (NADS) participates in the biosynthesis of nicotinamide adenine dinucleotide (NAD(+)) by transforming nicotinic acid adenine dinucleotide (NaAD) to NAD(+). The structural behavior of the active site, including stabilization of flexible loops 82-87 and 204-225, has been studied by determination of the crystal structures of complexes of NADS with natural substrates and a substrate analog. Both loops are stabilized independently of NaAD and solely from the ATP-binding site. Analysis of the binding contacts suggests that the minor loop 82-87 is stabilized primarily by a hydrogen bond with the adenine base of ATP. Formation of a coordination complex with Mg(2+) in the ATP-binding site may contribute to the stabilization of the major loop 204-225. The major loop has a role in substrate recognition and stabilization, in addition to the protection of the reaction intermediate described previously. A second and novel Mg(2+) position has been observed closer to the NaAD-binding site in the structure crystallized at pH 7.5, where the enzyme is active. This could therefore be the catalytically active Mg(2+).

Chlorination and nitration of soy isoflavones

Diets enriched in soy foods containing a high concentration of isoflavonoids are associated with a decrease in the incidence of several chronic inflammatory diseases. Studies with experimental models of diseases, such as atherosclerosis, suggest that these effects can be ascribed to the biological properties of the isoflavones. Since the isoflavones and tyrosine have structural similarities and modifications to tyrosine by inflammatory oxidants such as hypochlorous acid (HOCl) and peroxynitrite (ONOO(-)) have been recently recognized, we hypothesized that the isoflavones also react with HOCl and ONOO(-). Using an in vitro approach, we demonstrate in the present study that the isoflavones genistein, daidzein, and biochanin-A can be chlorinated and nitrated by these oxidants. These reactions were investigated using high-performance liquid chromatography, mass spectrometry, and nuclear magnetic resonance. In the reaction with HOCl, both mono- and dichlorinated derivatives of genistein and biochanin-A are formed, whereas with daidzein only a monochlorinated derivative was detected. The reaction between genistein or daidzein and ONOO(-) yielded a mononitrated product. However, no nitrated product was detected with biochanin-A. Furthermore, the reaction between genistein and sodium nitrite and HOCl yielded a chloronitrogenistein derivative, as well as a dichloronitrogenistein derivative. These results indicate that the ability of the isoflavones to react with these oxidant species depends on their structure and suggest that they could be formed under conditions where these reactive species are generated under pathological conditions.

Peptide inhibition of ENaC

Liddle's disease is an autosomal dominant form of human hypertension resulting from a basal activation of amiloride-sensitive Na+ channels (ENaC). This channel activation is produced by mutations in the beta- and/or gamma-carboxy-terminal cytoplasmic tails, in many cases causing a truncation of the last 45-76 amino acids. In this study, we tested two hypotheses; first, beta- and gamma-ENaC C-terminal truncation mutants (beta DeltaC and gamma DeltaC), in combination with the wild-type alpha-ENaC subunit, reproduce the Liddle's phenotype at the single channel level, i.e., an increase in open probability (Po), and second, these C-terminal regions of beta- and gamma-ENaC act as intrinsic blockers of this channel. Our results indicate that alpha beta DeltaC gamma DeltaC-rENaC, incorporated into planar lipid bilayers, has a significantly higher single channel Po compared to the wild-type channel (0.85 vs 0.60, respectively), and that 30-mer synthetic peptides corresponding to the C-terminal region of either beta- or gamma-ENaC block the basal-activated channel in a concentration-dependent fashion. Moreover, there was a synergy between the peptides for channel inhibition when added together. We conclude that the increase in macroscopic Na+ reabsorption that occurs in Liddle's disease is at least in part due to an increase in single channel Po and that the cytoplasmic tails of the beta- and gamma-ENaC subunits are important in the modulation of ENaC activity.

Adult spinal motoneurons remain viable despite prolonged absence of functional synaptic contact with muscle

Several rat medial gastrocnemius (MG) motor axons were allowed to regenerate into normally innervated muscle. Under these conditions, synapse formation is known to be prevented by the existence of the original innervation of the host muscle. A study was made of the ability of the implanted spinal motoneurons to acquire and retrogradely transport horseradish peroxidase (HRP) injected into the host muscle at various postoperative intervals. HRP-labeled MG motoneurons on the implanted side were observed at postoperative intervals as long as 290 days. A comparison of the number of labeled MG motoneurons on the implanted side versus the number on the unoperated, control side indicated no significant differences. At all investigated postoperative intervals except the earliest (7 DPO), a significant decrease in the mean MG motoneuron soma cross-sectional area was observed relative to the unoperated, control side. Analysis of labeled motoneuron size distributions showed that postoperative atrophy of larger, presumably alpha, motoneurons occurred at a significantly faster rate than in smaller, presumably gamma, motoneurons. These results demonstrate that axotomized adult spinal motoneurons survive and remain viable for prolonged periods when denied the opportunity to reinnervate muscle but do so in an atrophied state. The results indicate further that alpha and gamma motoneurons differ quantitatively in their responses to peripheral axotomy.

Axotomy-like changes in cat motoneuron electrical properties elicited by botulinum toxin depend on the complete elimination of neuromuscular transmission

The electrical properties of cat medial gastrocnemius (MG) spinal motoneurons were studied 14-21 d following injection of type A botulinum toxin (BTX) into the MG muscle. Treated MG muscles were atrophic, displayed pronounced fibrillation activity, and were markedly but not completely paralyzed. MG motoneuron electrical properties from animals with the highest MG muscle-twitch forces (greater than 20 gm) appeared normal, while motoneuron properties from animals with the lowest MG muscle-twitch forces (less than 10 gm) exhibited axotomy-like changes, though these changes were less pronounced than after axotomy itself. No changes in the axonal conduction velocity were observed, however. Motoneuron connectivity with MG muscle fibers was determined following intracellular stimulation of MG motoneurons by averaging EMG signals from 3 or 4 pairs of recording electrodes inserted into the BTX-treated MG muscles. Normal electrical properties were observed among motoneurons in which detectable EMG activity linked to the intracellular stimulation pulse was observed. The level of this connectivity, however, indicated that a relatively small number of muscle fibers were activated by individual motoneuron action potentials. Axotomy-like changes of electrical properties were observed in MG motoneurons that could not be associated with detectable EMG activity in the BTX-treated MG muscle following repeated trials of intracellular stimulation. These results indicate that the existence of effective neuromuscular transmission at a small number of motor terminals is sufficient to prevent the appearance of axotomy-like changes in motoneuron electrical properties, and that the absence of such transmission at all motor terminals is associated with the appearance of axotomy-like changes. The results suggest that the effects of axotomy itself on motoneuron properties may be based upon the loss or elimination of a potent interaction between muscle and motoneurons normally mediated by neuromuscular transmission.