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.     

Protein synthesis and secretion in the human epididymis and immunoreactivity with sperm antibodies

The synthesis and secretion of proteins in the different regions of the human epididymis were studied in vitro. Epididymal tissues obtained from patients undergoing castration for prostatic carcinoma or from cadavers were incubated in the presence of [35S]methionine, and the resulting radiolabeled proteins were analysed on SDS-PAGE. The corpus region was found to be the most active segment in total protein synthesis. Significant qualitative and quantitative changes were observed in the pattern of proteins secreted from the different epididymal regions. To establish those epididymal proteins that interact with maturing sperm, the secreted products were immunoreacted with antibodies raised against a Triton X-100 extract of ejaculated human sperm heads. The antibodies react mainly with the head region of ejaculated spermatozoa as judged by indirect immunofluorescence. Protein A-gold labeling of freeze-fracture images showed gold particle distribution on the sperm plasma membrane. Western blot analysis of the secreted proteins revealed four bands (66, 37, 32, and 29 kDa) in the proximal regions and six additional bands (80, 76, 48, 27, 22, and 17 kDa) in the distal part of the epididymis. Immunoprecipitation of the secreted proteins with these antibodies revealed six radioactive bands of 170, 80, 76, 60, 48, and 37 kDa, which indicates that certain proteins of epididymal origin bind to the sperm plasma membrane.     

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

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

Assessment of the Role of the Glutathione and Pentose Phosphate Pathways in the Protection of Primary Cerebrocortical Cultures from Oxidative Stress

Abstract: Reactive oxygen species have been implicated in neuronal injury associated with various neuropathological disorders. However, little is known regarding the relationship between antioxidant enzyme capacity and resultant toxicity. The antioxidant pathways of primary cerebrocortical cultures were directly examined using a novel technique that measures pentose phosphate pathway (PPP) activity, which is enzymatically coupled to glutathione peroxidase (GPx) detoxification of hydrogen peroxide (H₂O₂). PPP activity was quantified from data obtained by gas chromatography/mass spectrometry analysis of released labeled lactate following metabolic degradation of [1,6-¹³C₂,6,6-²H₂]glucose by cerebrocortical cultures. The antioxidant capacity of these cultures was systematically evaluated using H₂O₂, and the resultant toxicity was quantified by lactate dehydrogenase release. Exposure of primary mixed and purified astrocytic cultures to H₂O₂ caused stimulation of PPP activity in a concentration-dependent fashion from 0.25 to 22.2% and from 6.9 to 66.7% of glucose metabolized to lactate through the PPP, respectively. In the mixed cultures, chelation of iron before H₂O₂ exposure was protective and resulted in a correlation between PPP saturation and toxicity. Conversely, addition of iron, inhibition of GPx, or depletion of glutathione decreased H₂O₂-induced PPP stimulation and increased toxicity. These results implicate the Fenton reaction, reflect the pivotal role of GPx in H₂O₂ detoxification, and contribute to our understanding of the etiological role of free radicals in neuropathological conditions.     

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.     

Effects of plant size on photosynthesis and water relations in the desert shrub Prosopis glandulosa (Fabaceae)

The Jornada del Muerto basin of the Chihuahuan Desert of southern New Mexico, USA, has undergone a marked transition of plant communities. Shrubs such as mesquite (Prosopis glandulosa) have greatly increased or now dominate in areas that were previously dominated by perennial grasses. The replacement of grasses by shrubs requires an establishment phase where small shrubs must compete directly with similar-sized grass plants. This is followed by a phase in which large, established shrubs sequester nutrients and water within their biomass and alter soil resources directly under their canopy, creating “islands” of fertility. We hypothesized that these two phases were associated with shrubs having different physiological response capacities related to their age or size and the resource structure of the environment. As a corollary, we hypothesized that responses of small shrubs would be more tightly coupled to variation in soil moisture availability compared to large shrubs. To test these hypotheses, we studied gas exchange and water relations of small (establishing) and large (established) shrubs growing in the Jornada del Muerto as a function of varying soil moisture during the season. The small shrubs had greater net assimilation, stomatal conductance, transpiration, and xylem water potential than large shrubs following high summer rainfall in July, and highest seasonal soil moisture at 0.3 m. High rates of carbon assimilation and water use would be an advantage for small shrubs competing with grasses when shallow soil moisture was plentiful. Large shrubs had greater net assimilation and water-use efficiency, and lower xylem water potential than small shrubs following a dry period in September, when soil moisture at 0.3 m was lowest. Low xylem water potentials and high water-use efficiency would allow large shrubs to continue acquiring and conserving water as soil moisture is depleted. Although the study provides evidence of differences in physiological responses of different-sized shrubs, there was not support for the hypothesis that small shrubs are more closely coupled to variation in soil moisture availability than large shrubs. Small shrubs may actually be less coupled to soil moisture than large shrubs, and thus avoid conditions when continued transpiration could not be matched by equivalent water uptake.