The role of the cysteine-rich region of the β2 integrin subunit in the leukocyte function-associated antigen-1 (LFA-1, αLβ2, CD11a/CD18) heterodimer formation and ligand binding

The cysteine-rich region (CRR) of the β2 integrin subunit was replaced by that of β1 to give the chimera β2NV1. β2NV1 can combine with αL to form a variant leukocyte-function-associated antigen (LFA)-1 on COS cell surface, suggesting that the specificity of the β2 interaction with αL does not lie in the CRR. Unlike those expressing wild-type LFA-1, COS cells expressing αLβ2NV1 are constitutively active in intercellular adhesion molecule (ICAM)-1 adhesion. These results suggest that activation of LFA-1 involves the release of an intramolecular constraint, which is maintained, in part, by the authentic β2 CRR.     

Mechanism of action of ryanodine on cardiac sarcoplasmic reticulum

Ryanodine was found to initially inhibit calcium uptake by cardiac sarcoplasmic reticulum. This initial depression was followed by a later marked stimulation of calcium uptake. These effects were noted when calcium uptake was measured in the presence or absence of oxalate. The requirement for preincubation with ryanodine was highly dependent on ryanodine concentration and temperature. The mechanism of action of ryanodine clearly was not an effect on oxalate entry or calcium oxalate precipitation because the effects were also observed in the absence of oxalate. Ryanodine also had no effect on passive calcium efflux from actively loaded vesicles. Because ryanodine had no effect on Ca2+-ATPase activity under defined conditions of an ATP-regenerating system and no calcium gradient, we suggest ryanodine does not change the stoichiometry of the pump. Our results are consistent with the hypothesis that ryanodine closes a calcium channel in a subpopulation of the vesicles.     

Salt marsh harvest mouse demography and habitat use in the Suisun Marsh,California

We undertook a 2-year (2002–2004) mark–recapture study to investigate demographic performance and habitat use of salt marsh harvest mice (Reithrodontomys raviventris halicoetes) in the Suisun Marsh. We examined the effects of different wetland types and microhabitats on 3 demographic variables: density, reproductive potential, and persistence. Our results indicate that microhabitats dominated by mixed vegetation or pickleweed (Salicornia spp.) supported similar salt marsh harvest mouse densities, reproductive potential, and persistence throughout much of the year, whereas few salt marsh harvest mice inhabited upland grass-dominated microhabitats. We found that densities were higher in diked wetlands, whereas post-winter persistence was higher in tidal wetlands, and reproductive potential did not differ statistically between wetland types. Our results emphasize the importance of mixed vegetation for providing adequate salt marsh harvest mouse habitat and suggest that, despite their physiognomic and hydrological differences, both diked and tidal wetlands support salt marsh harvest mouse populations by promoting different demographic attributes. We recommend that habitat management, restoration, and enhancement efforts include areas containing mixed vegetation in addition to pickleweed in both diked and tidal wetlands. © 2011 The Wildlife Society.     

The unpredictability of favourability: condition assessment and protected areas in England

The probability that protected areas will deliver their potential for maintaining or enhancing biodiversity is likely to be maximised if they are appropriately and effectively managed. As a result, governments and conservation agencies are devoting much attention to the management of protected areas. In the U.K., the demand for performance accountability has resulted in Public Service Agreements (PSA) that set out targets for government departments to deliver results in return for investments being made. One such target for England is to ensure that all nationally important wildlife sites are in favourable condition by 2010. Here, we tested the hypothesis, of potential strategic importance, that the ecological condition of these sites is predictable from relationships with a range of physical, environmental and demographic variables. We used binary logistic regression to investigate these relationships, using the results of English Nature’s 1997–2003 condition assessment exercise. Generally, sites in unfavourable condition tend to be larger in area, located at higher elevations, but with higher human population density and are more spatially isolated from units of the same habitat. However, despite the range of different parameters included in our models, the extent to which the condition of any given site could be predicted was low. Our results have implications for the delivery of PSA targets, funding allocation, and the location of new protected areas.     

Quantifying the ion selectivity of the Ca2+ site in photosystem II: evidence for direct involvement of Ca2+ in O2 formation.

Calcium is an essential cofactor in the oxygen-evolving complex (OEC) of photosystem II (PSII). The removal of Ca2+ or its substitution by any metal ion except Sr2+ inhibits oxygen evolution. We used steady-state enzyme kinetics to measure the rate of O2 evolution in PSII samples treated with an extensive series of mono-, di-, and trivalent metal ions in order to determine the basis for the affinity of metal ions for the Ca2+-binding site. Our results show that the Ca2+-binding site in PSII behaves very similarly to the Ca2+-binding sites in other proteins, and we discuss the implications this has for the structure of the site in PSII. Activity measurements as a function of time show that the binding site achieves equilibrium in 4 h for all of the PSII samples investigated. The binding affinities of the metal ions are modulated by the 17 and 23 kDa extrinsic polypeptides; their removal decreases the free energy of binding of the metal ions by 2.5 kcal/mol, but does not significantly change the time required to reach equilibrium. Monovalent ions are effectively excluded from the Ca2+-binding site, exhibiting no inhibition of O2 evolution. Di- and trivalent metal ions with ionic radii similar to that of Ca2+ (0.99 A) bind competitively with Ca2+ and have the highest binding affinity, while smaller metal ions bind more weakly and much larger ones do not bind competitively. This is consistent with a size-selective Ca2+-binding site that has a rigid array of coordinating ligands. Despite the large number of metal ions that competitively replace Ca2+ in the OEC, only Sr2+ is capable of partially restoring activity. Comparing the physical characteristics of the metal ions studied, we identify the pK(a) of the aqua ion as the factor that determines the functional competence of the metal ion. This suggests that Ca2+ is directly involved in the chemistry of water oxidation and is not only a structural cofactor in the OEC. We propose that the role of Ca2+ is to act as a Lewis acid, binding a substrate water molecule and tuning its reactivity.