Structure/activity relationships in the arginine taste pathway of the channel catfish

To characterize the molecular/structural requirements for activationor antagonism of the arginine taste pathways in catfish, Ictaluruspunctatus, structure/activity studies were performed using integratedmultiunit responses and cross-adaptation. Of all the guanidinium-containingcompounds tested, only L-arginine, L--amino-ß-guanidinopropionic acid (L-AGPA) and L-arginine methyl and ethyl esterswere strong stimuli. Results of functional group substitutionsand modification of the L-arginine parent molecule indicatedthat: (i) stereospecificity was observed with D-arginine beinga much less effective stimulus than L-arginine; (ii) an L-aminogroup must be present and unblocked (-chloro-guanidino-N-valericacid and N-acetyl L-arginine were weak or inactive stimuli);(iii) a free carboxylic acid group was not necessary for activity;(iv) the distance between the anomeric carbon and the guanidiniumgroup was not critical (L-AGPA, having two methylene groupsless than L-arginine was a moderately strong stimulus as wasL-canavanine) and (v) modification or substitution of the guanidinumgroup by other basic groups including amine, methyl or dimethylamineor by an isosterc (ureido) resulted in loss of stimulatory ability.In general, those stimuli and analogs that were good cross-adaptersof L-arginine stimulation were also good competitors for L-[³H]argininebinding to a partial membrane fraction (P2) from catfish tasteepithelium. On the other hand, compounds that were poor cross-adaptingstimuli were also poor binding competitors. While D-argininewas a poor stimulus, it did cross-adapt L-arginine and competedwell with L-[³H]arginine for binding to fraction P2.     

The effects of a glycerin-based blood analog on the testing of bioprosthetic heart valves

Detailed comparisons of aortic valvular flow using saline, with that using a glycerin-based blood analog in a pulse duplicator are reported. The experiments were carried out to determine whether exposure to glycerin caused stiffening of bioprosthetic valve leaflets. For two pericardial bioprostheses and for a mechanical valve we observed a fluid-dependent systolic volume flow, a fluid-dependent regurgitation volume, and fluid-dependent systolic pressure differences. Volume flow changes, both forward and reverse, are independent of valve type. The observed pressure differences, while proportional to fluid density for the mechanical valve, are fluid dependent in a more complicated way for the pericardial valves. However, no trend of changing valvular performance was observed over as much as 80 days of glycerin exposure, indicating that it is unlikely that the fluid-dependent performance was caused by glycerin absorption by the valve leaflets. We conclude that valid performance comparisons between mechanical and bioprosthetic valves may be made using a glycerin-based fluid. Furthermore, it appears that any detailed analysis of the physical mechanisms of valvular flow dissipation will require a properly matched blood analog.     

MPphiWR-2, a cryptic phage associated withMicromonospora purpurea ATCC 15835

Summary A previously undescribed cryptic phage was found associated withMicromonospora purpurea ATCC 15835.     

Moral commitment without objectivity or illusion: Comments on Ruse and Woolcock

Peter Woolcock, in Ruse's Darwinian Meta-Ethics: A Critique, argues that the subjectivist (nonobjectivist) Darwinian metaethics proposed by Michael Ruse (in Taking Darwin Seriously) cannot work, because the illusion of objectivity that Ruse claims is essential to morality breaks down when it is recognized as illusion, and there then remain no good reasons for acknowledging or following moral obligations. Woolcock, however, is mistaken in supposing that moral behaviour requires rational motivation. Ruse's Darwinian metaethical analysis shows why such objective support for morality is neither plausible nor necessary; and when that is recognized, it can also be seen that Ruse's proposed illusion of moral objectivity is superfluous.     

PrP in pathology and pathogenesis in scrapie-infected mice

PrP accumulation in the brains of mice infected with scrapie takes several different forms: amyloid plaques, widespread accumulation in neuropile, and perineuronal deposits. PrP is also sometimes detected within microglia and in or around astrocytes. There are dramatic and reproducible differences between scrapie strains in the relative prominence of these changes and their distribution in the brain. Depending on the scrapie strain, PrP pathology is targeted precisely to particular brain areas, often showing a clear association with identifiable groups of neurons. These results suggest that PrP changes are primarily associated with neurons, and that different scrapie strains recognize and selectively replicate in different populations of neurons. Immunostaining at the ultrastructural level demonstrates an association of PrP with neurite plasmalemma, around amyloid plaques, and in areas of widespread neuropile and perineuronal accumulation. It is probable that PrP is encoded by theSinc gene, which controls the incubation period of scrapie in mice. Studies using the intraocular infection route show that theSinc gene controls the onset rather than the rate of replication, suggesting that PrP may be involved in cell-to-cell spread of infection. The accumulation of PrP at the surface of neurons is consistent with such a role.     

Congruent evolution between whiteflies (Homoptera: Aleyrodidae) and their bacterial endosymbionts based on respective 18S and 16S rDNAs

Whiteflies (family Aleyrodidae) possess heritable eubacterial endosymbionts sustained in specialized organ-like structures called mycetomes. Comparisons of distances between the ash whitefly,Siphoninus phillyreae, and two biotypes (A and B) of the sweetpotato whitefly,Bemisia tabaci, based on sequence analysis of genes for 18S rRNAs (rDNAs), were equivalent to the distances represented by the 16S rDNAs of their respective endosymbionts. This finding indicates that evolutionary divergence in whitefly hosts and their endosymbionts is congruent. The nucleotide sequences of the 18S rDNAs and endosymbiont 16S rDNAs indicate the two biotypes ofB. tabaci are the same species.