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.     

Nonreceptor-mediated responses of adenylate cyclase in membranes from liver, muscle, and white and brown adipose tissue of obese (fa/fa) and lean (Fa/) Zucker rats

Adenylate cyclase activity was determined in membranes of liver, muscle, white adipose tissue, and brown adipose tissue (BAT) of lean (Fa/) and obese (fa/fa) Zucker rats. Responses were monitored following beta-adrenergic receptor stimulation and addition of GTP, GTP gamma S, or forskolin. beta-Adrenergic responses in liver, white adipose tissue, and BAT were lower in obese than in lean animals. No such difference was observed in muscle membranes. Production of cAMP after addition of guanine nucleotides was lower in liver and white adipose tissue membranes from obese rats compared with their lean littermates. Synthesis of cAMP in muscle membranes of obese animals after addition of GTP was either not different, or slightly higher, than that observed in muscle membranes from lean animals. Furthermore, production of cAMP after forskolin addition to muscle membranes of obese rats was significantly higher than that observed from lean rats under the same conditions. Interestingly, BAT membranes of obese rats were significantly more sensitive to guanine nucleotide activation than those of lean animals. The results confirm recent findings indicating inferior function of G proteins in liver plasma membranes of obese Zucker rats, and extend this observation to adipose tissue. The present results further suggest that the "nonreceptor" components (e.g., G proteins) responsible for the activation of adenylate cyclase in BAT membranes of obese rats are more responsive to stimulation than those of lean animals. Such sensitivity may be related to and perhaps compensate for the reduced thermogenic activity in the obese Zucker rat during the development of obesity.     

Increased Resistance Against Oxidative Stress Is Observed During A Short Period of Renal Reperfusion After A Temporal Ischaemia

Reperfusion of rat kidney submitted to temporal ischaemia induces a decrease in glutathione content. Lipid peroxidation is not detected in kidney homogenates but microsomes obtained after periods of reperfusion longer than 60 minutes show increased malondialdehyde values correlated with high oxygen consumption and superoxide free radical generation. Microsomes obtained from kidneys submitted to 15 or 60 minutes of reperfusion are resistant to NADPH-induced lipid peroxidation but after 120 minutes of reperfusion an increased lipid peroxidative response is observed. Although the mechanism of the protection found in microsomes against the induction of oxidative stress in the first 60 minutes of reperfusion is unknown, it is postulated that this subcellular fraction plays an important role in the oxidative stress observed after longer periods of reperfusion.     

THERMAL EVOLUTION OF EGG SIZE IN DROSOPHILA MELANOGASTER

We measured the size of eggs produced by populations of Drosophila melanogaster that had been collected along latitudinal gradients in different continents or that had undergone several years of culture at different temperatures in the laboratory. Australian and South American populations from higher latitudes produced larger eggs when all were compared at a standard temperature. Laboratory populations that had been evolving at 16.5°C produced larger eggs than populations that had evolved at 25°C or 29°C, suggesting that temperature may be an important selective agent in producing the latitudinal clines. Flies from laboratory populations produced larger eggs at an experimental temperature of 16.5°C than at 25°C, and there was no indication of genotype-environment interaction for egg size. Evolution of egg size in response to temperature cannot be accounted for by differences in adult body size between populations. It is not clear which life-history traits are direct targets of thermal selection and which are showing correlated responses, and disentangling these is a task for the future.     

Biological basis for the management of ‘lugs negra’ (Sarcothalia crispata Gigartinales,Rhodophyta) in southern Chile

The present paper describes growth dynamics in a natural bed of the resource luga negra (Sarcothalia crispata) in Guapilinao, southern Chile (41°57 S, 73°31 W). This resource is currently harvested and exported as raw material for the production of carrageenan. Seasonal variation in biomass, frond size, density and phenology was determined by periodic sampling. Natural recruitment was evaluated on different substrata added to the field; at the same time, substrata were inoculated under greenhouse conditions. Results showed that luga negra has seasonal growth: biomass increased from a minimum in spring to a maximum in mid to late summer. On the other hand, density was minimal in winter (200 ind. m^–2) and increased to 2000 ind. m^–2 in late spring. Peak abundance of mature tetrasporic fronds occurred in late summer, whereas that of cystocarpic fronds occurred in winter. Recruitment began in summer and extended into winter. Survival on different substrata were compared. Gametophytes had better survival rates on clam shells and 5 mm rope while tetrasporophytes had the best survival rate on clam shells and secondarily on boulders.     

Modeling competition between Laurencia obtusa (Ceramiales,Rhodophyta) and Hypnea spinella (Gigartinales,Rhodophyta) at Cabo Frio Island,Rio de Janeiro,Brazil

The Lotka-Volterra competition model was used to represent the interaction between Laurencia obtusa and Hypnea spinella. A new model that considers effects of competition on algal carrying capacity is suggested. To test the models, data from field experiments conducted in an intertidal region at Cabo Frio Island, Rio de Janeiro, Brazil, were used. Both models showed that Hypnea was a stronger competitor than Laurencia. The model of interaction through the carrying capacity showed a stable coexistence between the algal populations and better represented the experimental data.     

Variable influence of ferric and cupric ions on Saccharomyces cerevisiae strains used in asymmetric organic synthesis

Summary Fe (III) and Cu (II) each at 50 M in four commercial strains of Saccharomyces cerevisiae induced an increase of NAD(P)⁺ reduction in one strain (Turkish), but two others (Chilean and Brazilian), the presence of Fe(III) and/or Cu(II) diminished NAD(P)⁺ reduction presumably due to free radicais formation inside these living cells. Suprisingly, in the American strain, Fe(III) induced a decrease and Cu (II) an increase of NAD(P)⁺ reduction.     

Factors affecting transient gene expression in cultured radiata pine cotyledons following particle bombardment

Transfer and expression of the β–glucuronidase gene ( gusA ) in cultured cotyledons of radiata pine ( Pinus radiata D. Don ) were obtained by particle bombardment. Conditions for optimum transient expression were established by using plasmid pB[/12], delivered by gold particles, 1.6 μm in diameter, into 8-day-old cultured cotyledons. Helium pressure of 7.6 MPa, bombardment distance between the stopping screen and the target tissues of 6 cm, and 0.8 μg of plasmid DNA per bombardment proved to be the best parameters for transient expression; using these parameters 79% of bombarded cotyledons showed GUS activity, with 4.3 blue spots per cotyledon. This system was used for studying the expression of several gus-driven promoters the expression of the sunflower ubiquitin gene promoter was higher (99% of positive cotyledons, with 14.2 blue spots per cotyledon) than that of the CaMV 35S promoter, whereas the rice actin and the maize alcohol dehydrogenase gene promoters gave lower gusA expression, as determined histochemically. These results were confirmed by using the gus fluorometric assay. Use of the sunflower ubiquitin gene promoter resulted in gusA expression up to 20 days after bombardment, with a significant level of gus expressing loci per bombarded cotyledon, whereas with the CaMV 35S promoter gusA expression was lost 12 days after bombardment.     

A survey of alkaloids in the genera Harpalyce and Brongniartia (Fabaceae—Brongniartieae)

The presence of alkaloids in six species of Brongniartia and three species of Harpalyce is reported. This survey revealed remarkable qualitative differences in the alkaloid profiles of these two genera. B. discolor, B. lupinoides, B. sousae and B. intermedia showed a typical -pyridone pattern, with cytisine, anagyrine and baptifoline as major alkaloids. In leaves of the first three species ormosanine-type alkaloids occurred additionally. B. flava and B. vazquezii are devoid of -pyridones, but accumulate lupanine, hydroxylated lupanines and ester alkaloids. All three species of Harpalyce were similar in accumulating -pyridones, but H. formosa differed from H. brasiliana and H. pringlei in the presence of epilupinine. In general the alkaloid profiles of Brongniartia and Harpalyce show similarities to those of the Australian genera Hovea, Lamprolobium, Plagiocarpus and Templetonia and support therefore the actual concept of the enlarged tribe Brongniartieae.