Changes of polymerization and conformation of hemoglobin S induced by thiol reagents

Thiol reagents, covalently bound to cysteine beta 93, either inhibit or facilitate the polymerization process of hemoglobin S. The progelling effect of parahydroxymercurybenzoate or 2,2'-dithiodipyridine contrasted with the increased oxygen affinity and the destabilization of the T state of Hb shown by functional and NMR studies. Thiol reagents increased the oxygen affinity of Hb from 30 to 1000%. Such variability was also observed in the reduction (up to 50%) of the alkaline Bohr effect. We show that the antigelling or progelling activity of thiol reagents does not depend solely on the concentration of molecules present in the deoxy T state but that specific effects of the reagent affects molecular interactions of the hemoglobin S polymerization process.     

Ageing of ungulate pellets in semi-arid landscapes: how the shade of colour can refine pellet-group counts

Pellet-group counts can be useful in monitoring ungulate population trends, particularly in elusive species. In semi-arid areas, ambient conditions conserve the pellets during the dry season. Thus, dating of accumulated pellet groups should be helpful in approximating the numbers of ungulates present during any chosen part of the dry season. The aims of this study were to confirm that the decay rate of pellet groups was low during the dry season, to identify the major causes of decay and to test the usefulness of criteria, easily measurable in the field, in dating pellets. Every month during the dry season pellet groups of five African savanna ungulates were collected fresh and deposited on bare ground at an experimental site. The levels of hardness, cracking, scattering, attack by insects and shade of colour of the pellets were monitored until the rainy season started. As expected, only a few pellet groups decayed completely during the dry season. The pellets’ shade of colour was the best criterion to date them. We discuss pellet colour as an original tool for monitoring the trends in ungulate use of target areas in semi-arid environments.     

The social environment influences the behavioural responses of beef cattle to handling

In cattle, a gregarious species, the social group influences individual stress responses to fear-eliciting situations. As handling can be stressful for farm animals, it can be hypothesised that social partners modify individual responses to handling. The present experiment investigated the effect of the presence or absence of social partners on behavioural reactions of beef calves in a handling test. At the age of 10 months, 38 calves from two breeds (Salers and Limousine) were individually subjected to the docility test, once while in visual contact with four familiar peers, and once in the absence of peers, following a crossover design. The docility test procedure included physical separation from peers (30 s; period 1), exposition to a stationary human (30 s; period 2), and handling by human (30 s-2.5 min, according to the success in handling; period 3). In absence of human (period 1), calves in visual contact with their peers spent more time motionless than when peers were totally absent (P<0.001). The social environment also influenced the duration of handling (period 3); the human required more time to successfully handle calves when peers were present (P<0.05). In conclusion, the presence of peers affects individual calves' reactions to the docility test.     

Cleavage properties of an archaeal site-specific recombinase, the SSV1 integrase

SSV1 is a virus infecting the extremely thermophilic archaeon Sulfolobus shibatae. The viral-encoded integrase is responsible for site-specific integration of SSV1 into its host genome. The recombinant enzyme was expressed in Escherichia coli, purified to homogeneity, and its biochemical properties investigated in vitro. We show that the SSV1 integrase belongs to the tyrosine recombinases family and that Tyr(314) is involved in the formation of a 3'-phosphotyrosine intermediate. The integrase cleaves both strands of a synthetic substrate in a temperature-dependent reaction, the cleavage efficiency increasing with temperature. A discontinuity was observed in the Arrhenius plot above 50 degrees C, suggesting that a conformational transition may occur in the integrase at this temperature. Analysis of cleavage time course suggested that noncovalent binding of the integrase to its substrate is rate-limiting in the cleavage reaction. The cleavage positions were localized on each side of the anticodon loop of the tRNA gene where SSV1 integration takes place. Finally, the SSV1 integrase is able to cut substrates harboring mismatches in the binding site. For the cleavage step, the chemical nature of the base in position -1 of cleavage seems to be more important than its pairing to the opposite strand.     

Glutamate optimizes enzymatic activity under high hydrostatic pressure in Desulfovibrio species: effects on the ubiquitous thioredoxin system

Extremophiles - In piezophilic microorganisms, enzymes are optimized to perform under high hydrostatic pressure. The two major reported mechanisms responsible for such adaptation in bacterial...