Occurrence of fleshy fungi from agricultural fields

Thirteen species of fleshy fungi were identified from two agricultural fields during the 1989 and 1990 growing seasons at the Rural Development Center (RDC) and Horticulture Farm, Coastal Plain Experiment Station, Tifton, Georgia. The three most common fungi wereCoprinus plicatilis, Cyathus olla, andPanaeolina foenisecii. At the former site, residue management practices were established for evaluating crop production and at the Horticulture Farm different crops were grown with conservation tillage employing a Low Input Sustainable Vegetable Production system. Tillage treatments at the RDC were no-till, row-till, ridge-plant, and moldboard-plowing. Residue management of triticale included burning or cutting the stubble at a height of 20 or 60 cm at harvest. At the Horticulture Farm, seven winter cover crops were compared to a fallow control. No significant differences were shown between observations of fungal species and individual treatments at the Horticulture Farm during 1989 and 1990. However, there were treatment differences for observed fungi at the RDC farm on specific dates for both years. Furthermore, no individual treatment(s) during the investigation increased observation rates of specific fungal species. Non-burned debris treatments showed consistently higher populations and diversity of fungi than burn debris plots.     

The effect of dichloroacetate on the isolated no flow arrested rat heart

Ischemic dysfunction, including contracture, has been attributed to lack of ATP, although previous work has not been consistent with this concept. We describe here a model of no flow ischemic arrest, characterized by depressed levels of mechanical function upon reperfusion and high energy phosphate stores within normal limits. The decreased mechanical function bears an inverse relationship to myocardial lactate levels after twenty-minutes of reperfusion in the absence or presence of dichloroacetic acid (DCA). Post-ischemic non-DCA treated hearts attained peak work of only 25% of that of controls, while those treated with DCA following ischemia performed almost as well as controls. ATP and CP levels remained high in both DCA treated and non-DCA treated hearts. Lactate levels were high in hearts immediately following ischemia, but were reduced to control levels in post-ischemic hearts perfused with DCA within twenty minutes, whereas those not treated with DCA had lactate levels two to three times that of controls within the same time period. Pyruvate dehydrogenase (PDH) activity was reduced in non-DCA treated post ischemic hearts after twenty minutes reperfusion but was elevated above controls in hearts reperfused with DCA. The data indicates that DCA increases mechanical performance of the isolated post-ischemic rat heart and the proposed mechanism for this increase is the oxidative removal of lactate resulting from an increase in PDH activity.     

Vulnerability of sea hares to fish predators: importance of diet and fish species

Many sea hares (Opisthobranchia, Anaspidea) sequester secondary metabolites from their algal diets. Tests of the hypothesis that sequestered metabolites deter predators have yielded ambiguous results. We manipulated secondary metabolites in vivo by collecting the sea hare Stylocheilus striatus from different host algae, and by raising it in the laboratory on artificial diets containing or lacking secondary metabolites (malyngamides A and B). Sea hares were then offered to fish. Fish identity affected vulnerability of sea hares to predation far more than did diet history. Wrasses and bream ate most sea hares tasted; damselfishes, goatfishes, and other fishes rejected most. Diet history affected vulnerability of sea hares to wrasses in one of four experiments, and if data from all experiments were pooled, but the effect was modest. Diet history did not affect vulnerability of sea hares to other fish taxa. Despite several studies, evidence for diet-derived defenses against predators in sea hares remains equivocal.     

Endothelin produces pulmonary vasoconstriction and systemic vasodilation

Endothelin is a newly described polypeptide derived from endothelial cells. The effects of porcine endothelin on the pulmonary vascular bed and systemic vascular bed were investigated in the anesthetized, intact-chest cat under conditions of constant pulmonary blood flow and left atrial pressure. Intralobar bolus injections of porcine endothelin (100-1000 ng) produced a mild vasoconstrictor response in the pulmonary vascular bed. The pulmonary vasoconstrictor response to endothelin was not altered when pulmonary vasomotor tone was increased by infusion of U46619. In contrast to this mild pulmonary vasoconstrictor response, endothelin decreased systemic arterial pressure. Moreover, injections of porcine endothelin into the right and left atria produced similar reductions in aortic pressure as well as similar increases in cardiac output and decreases in systemic vascular resistance. The systemic vasodilator response to porcine endothelin was not affected by beta 2-adrenoceptor blockade. The present data suggest that endothelin does not undergo significant first-pass pulmonary metabolism. The pulmonary vasoconstrictor response to bolus injections of porcine endothelin is not altered by changes in pulmonary vasomotor tone. In contrast, endothelin markedly dilated the systemic vascular bed independently of activation of beta 2-adrenoceptors. The present study provides the first report of the activity of endothelin on pulmonary and systemic hemodynamics in vivo. Moreover, the potent vasodilator activity of endothelin in the systemic vascular bed and its weak effect on pulmonary vessels suggest that endothelin may be more important in the regulation of peripheral vasomotor tone than the pulmonary vascular bed.     

Characterization of a new AAA+ protein from archaea

We investigated a new archaeal member of the AAA+ protein family (ATPases associated with various cellular activities) which is found in all methanogenic archaea and the sulphate-reducer Archaeoglobus fulgidus. These proteins cluster to COG1223 predicted to form a subgroup of the AAA+ ATPases. The gene from A. fulgidus codes for a protein of 40 kDa monomeric molecular weight, which we overexpressed in Escherichia coli and purified to homogeneity. The protein forms ring-shaped complexes with a diameter of 125A as determined by electron microscopy. Using sedimentation equilibrium analysis we demonstrate that it assembles into hexamers over a wide concentration range both in presence and absence of ATP. As suggested by homology to other members of the AAA+ family, the complex binds and hydrolyzes ATP. Michaelis-Menten analysis revealed a k(cat) of 118 min(-1) and a K(M) of 1.4 mM at 78 degrees C. This hyperthermophilic archaeal ATPase is stable to 86 degrees C and the ATPase activity is maximal at this temperature. The protein is most homologous to the AAA-domain of FtsH from bacteria, while the N-terminal domain shows predicted structural homology to members of the CDC48 family of AAA proteins. Possible roles of this new AAA+ protein are discussed.     

Structure of the 21-30 fragment of amyloid beta-protein

Folding and self-assembly of the 42-residue amyloid beta-protein (Abeta) are linked to Alzheimer's disease (AD). The 21-30 region of Abeta, Abeta(21-30), is resistant to proteolysis and is believed to nucleate the folding of full-length Abeta. The conformational space accessible to the Abeta(21-30) peptide is investigated by using replica exchange molecular dynamics simulations in explicit solvent. Conformations belonging to the global free energy minimum (the "native" state) from simulation are in good agreement with reported NMR structures. These conformations possess a bend motif spanning the central residues V24-K28. This bend is stabilized by a network of hydrogen bonds involving the side chain of residue D23 and the amide hydrogens of adjacent residues G25, S26, N27, and K28, as well as by a salt bridge formed between side chains of K28 and E22. The non-native states of this peptide are compact and retain a native-like bend topology. The persistence of structure in the denatured state may account for the resistance of this peptide to protease degradation and aggregation, even at elevated temperatures.     

The Structure of Aβ42 C-Terminal Fragments Probed by a Combined Experimental and Theoretical Study

The C-terminus of amyloid β-protein (Aβ) 42 plays an important role in this protein's oligomerization and may therefore be a good therapeutic target for the treatment of Alzheimer's disease. Certain C-terminal fragments (CTFs) of Aβ42 have been shown to disrupt oligomerization and to strongly inhibit Aβ42-induced neurotoxicity. Here we study the structures of selected CTFs [Aβ(x-42); x = 29-31, 39] using replica exchange molecular dynamics simulations and ion mobility mass spectrometry. Our simulations in explicit solvent reveal that the CTFs adopt a metastable β-structure: β-hairpin for Aβ(x-42) (x = 29-31) and extended β-strand for Aβ(39-42). The β-hairpin of Aβ(30-42) is converted into a turn-coil conformation when the last two hydrophobic residues are removed, suggesting that I41 and A42 are critical in stabilizing the β-hairpin in Aβ42-derived CTFs. The importance of solvent in determining the structure of the CTFs is further highlighted in ion mobility mass spectrometry experiments and solvent-free replica exchange molecular dynamics simulations. A comparison between structures with solvent and structures without solvent reveals that hydrophobic interactions are critical for the formation of β-hairpin. The possible role played by the CTFs in disrupting oligomerization is discussed.