Differences in the Activation of the Mitochondrial Permeability Transition Among Brain Regions in the Rat Correlate with Selective Vulnerability

Mitochondria from different regions of the brain were prepared, and the activation of the mitochondrial permeability transition (MPT) by calcium was investigated by monitoring the associated mitochondrial swelling. In general, the properties of the MPT in brain mitochondria were found to be qualitatively similar to those observed in liver and heart mitochondria. Thus, swelling was inhibited by adenine nucleotides (AdNs) and low pH (<7.0), whereas thiol reagents and alkalosis facilitated swelling. Cyclosporin A and its nonimmunosuppressive analogue N-methyl-Val-4-cyclosporin A (PKF 220-384) both inhibited swelling and prevented the translocation of cyclophilin D from the matrix to the membranes of cortical mitochondria. However, the calcium sensitivity of the MPT differed in mitochondria from three brain regions (hippocampus > cortex > cerebellum) and is correlated with the susceptibility of these regions to ischemic damage. Depleting mitochondria of AdNs by treatment with pyrophosphate ions sensitized the MPT to [Ca2+] and abolished regional differences, implying regional differences in mitochondrial AdN content. This was confirmed by measurements showing significant differences in AdN content among regions (cerebellum > cortex > hippocampus). Our data add to recent evidence that the MPT may be involved in neuronal death.     

Structural features of the antibody-A chain linkage that influence the activity and stability of ricin A chain immunotoxins.

The importance of the various structural elements constituting a ricin A chain immunotoxin to the stability of the disulfide bond between the antibody and A chain was examined using a panel of immunoconjugates prepared with the mouse monoclonal antibody Fib75. Analogues of the standard ricin A chain immunotoxin prepared with the N-succinimidyl 3-(2-pyridyldithio)propionate disulfide cross-linker included immunoconjugates made with N-succinimidyl 4-[(iodoacetyl)amino]benzoate the thioether cross-linker; with N-succinimidyl 3-(2-pyridyldithio)butyrate, the hindered disulfide cross-linker; with a peptide spacer between the antibody and cross-linker; or with the dodecapeptide corresponding to the C-terminus of ricin A chain. The cytotoxic activities of the immunoconjugates and their susceptibility to reduction by glutathione in vitro were compared. The thioether-linked immunotoxin could not be cleaved by glutathione in vitro and had low cytotoxic potency, consistent with the requirement of a reducible disulfide linkage for activity. The hindered disulfide-linked immunotoxin was 3-fold more stable to reduction than the immunotoxin containing a standard unhindered disulfide linkage, but the cytotoxic activities of the two constructs were indistinguishable. The introduction of a flexible peptide Ala-Ala-Pro-Ala-Ala-Ala-Pro-Ala-Pro-Ala between Fib75 and the disulfide linkage introduced by SPDP had no deleterious effect on cytotoxic activity and no effect on the susceptibility of the disulfide linkage to reduction. This finding suggests that the enforced proximity of the A chain to the antibody caused by the use of a short chemical cross-linker in a conventional immunotoxin has no influence on either of these properties in this system.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regulation of Cadherin Trafficking

Cadherins are a large family of cell–cell adhesion molecules that tether cytoskeletal networks of actin and intermediate filaments to the plasma membrane. This function of cadherins promotes tissue organization and integrity, as demonstrated by numerous disease states that are characterized by the loss of cadherin-based adhesion. However, plasticity in cell adhesion is often required in cellular processes such as tissue patterning during development and epithelial migration during wound healing. Recent work has revealed a pivotal role for various membrane trafficking pathways in regulating cellular transitions between quiescent adhesive states and more dynamic phenotypes. The regulation of cadherins by membrane trafficking is emerging as a key player in this balancing act, and studies are beginning to reveal how this process goes awry in the context of disease. This review summarizes the current understanding of how cadherins are routed and how the interface between cadherins and membrane trafficking pathways regulates cell surface adhesive potential. Particular emphasis is placed on the regulation of cadherin trafficking by catenins and the interplay between growth factor signaling pathways and cadherin endocytosis.     

Minimizing the cost of environmental management decisions by optimizing statistical thresholds

Environmental management decisions are prone to expensive mistakes if they are triggered by hypothesis tests using the conventional Type I error rate (α) of 0.05. We derive optimal α‐levels for decision‐making by minimizing a cost function that specifies the overall cost of monitoring and management. When managing an economically valuable koala population, it shows that a decision based on α = 0.05 carries an expected cost over $5 million greater than the optimal decision. For a species of such value, there is never any benefit in guarding against the spurious detection of declines and therefore management should proceed directly to recovery action. This result holds in most circumstances where the species’ value substantially exceeds its recovery costs. For species of lower economic value, we show that the conventional α‐level of 0.05 rarely approximates the optimal decision‐making threshold. This analysis supports calls for reversing the statistical ‘burden of proof’ in environmental decision‐making when the cost of Type II errors is relatively high.     

Synthesis and structure–activity relationship of 2-arylamino-4-aryl-pyrimidines as potent PAK1 inhibitors

2-Arylamino-4-aryl-pyrimidines were found to be potent inhibitors of PAK1 kinase. The synthesis and SAR are described. The incorporation of a bromide at the 5-position of the pyrimidine core and in combination with a 1,2-dimethylpiperazine pendant domain yielded a lead compound with potent PAK1 inhibition and anti-proliferative activity in various colon cancer cell lines.     

Biosynthesis of trichothecene mycotoxins: cell-free epoxidation of a trichodiene derivative

A cell-free enzyme system from cultures of Fusarium culmorum catalyses the 12,13-epoxidation of semi-synthetic 9 beta,10 beta-epoxytrichodiene to 9 beta,10 beta;12,13-diepoxytrichodiene. This enzyme activity may be involved in the biosynthesis of trichothecene mycotoxins and since the 12,13-epoxide is known to be essential for toxicity, the enzyme activity probably confers the toxic properties associated with this group of mycotoxins. The epoxidase requires NADPH and molecular oxygen, is inhibited by carbon monoxide, and thus appears to be a cytochrome P-450-dependent mono-oxygenase. Whole cell cultures of the fungus carry out the same biotransformation, and in addition hydroxylate the diepoxide product at position 3, yielding 3 alpha-hydroxy-9 beta,10 beta;12,13-diepoxytrichodiene.     

Isolation from sugarcane cultures of variants resistant to antimetabolites

Variants resistant to antimetabolites are useful for investigating metabolic regulation and biochemical genetics in organisms. In this study, suspensions of mutagenized sugarcane ( Saccharum sp.) cells, originating from a stalk parenchyma explain of the Hawaiian variety 50–7209, were used to investigate the feasibility of isolating variants resistant to l -canavanine, glyphosate [N-(phosphonomethyl)glycine], ophiobolin A and orthovanadate. Rigorous retesting of clones which grew on selection media led to the identification of three cell lines, two of which were resistant to glyphosate and one to orthovanadate. No variants were isolated which showed a persistent resistance either to l -canavanine or ophiobolin A.
The results demonstrate that resistant variants do occur, or can be induced, in sugarcane cell suspensions and that they can be rescued and cultivated.     

Allometric scaling of maximum population density: a common rule for marine phytoplankton and terrestrial plants

A primary goal of macroecology is to identify principles that apply across varied ecosystems and taxonomic groups. Here we show that the allometric relationship observed between maximum abundance and body size for terrestrial plants can be extended to predict maximum population densities of marine phytoplankton. These results imply that the abundance of primary producers is similarly constrained in terrestrial and marine systems by rates of energy supply as dictated by a common allometric scaling law. They also highlight the existence of general mechanisms linking rates of individual metabolism to emergent properties of ecosystems.