Evidence suggesting direct oxidation of human erythrocyte membrane sulfhydryls by copper

Results are presented which suggest that cupric ion can directly oxidize the sulfhydryls of human erythrocyte membrane proteins leading to the formation of disulfide links. When packed ghosts were incubated in cupric sulfate (0.3 to 0.7 mM) at pH 8, and electrophoresed on sodium dodecyl sulfate polyacrylamide gels in the absence of dithiothreitol bands 1, 2 (spectrin); 4.2 and 5 (actin) diminished in intensity concomitant with the appearance of high molecular weight material. Band 3 moved to its dimeric position on the gel. Evidence that these crosslinks result from formation of new disulfide links due to direct copper binding includes: (a) reversal of crosslinking upon addition of dithiothreitol; (b) blockage of the effect by N-ethylmaleimide, EDTA and mercuric chloride. The effect of copper was observed under N₂, suggesting that it is not related to air oxidation. Furthermore, the crosslinking effect does not require high copper concentrations if the ghost concentration is low. The possible implication of these results with regard to copper induced hemolytic anemias is briefly discussed.     

Mark-resight estimates of seasonal variation in harbor seal abundance and site fidelity

Monitoring trends in abundance of pinnipeds typically involves counting seals at terrestrial haul-out sites during the breeding season. Counts of seals made at other times of the year are typically lower; however, it is often unknown whether this is because fewer animals are present or whether lower counts simply reflect a reduction in haul-out probability. Here we illustrate how photo-identification data from an individual-based study of harbor seals (Phoca vitulina) can be used to estimate seasonal variation in abundance and site fidelity. Monthly data collected over a two-year period were analyzed using a mark-recapture mark-resight model accounting for individuals transitioning between observable and unobservable states. Levels of site fidelity were high throughout the year and abundance estimates showed no seasonal pattern. This suggests that individual seals used haul-out sites to the same extent throughout the year, and that peaks in counts during the breeding season are a result of seasonal changes in haul-out probability. The results of this study have implications for understanding population sub-structuring, gene flow and disease spread.