. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. TEMPERATURE SENSITIVITY OF HEMOCYANINS 159 5 - Cancer anthonyi £ 7> o 8#* • o <*A • * o £ • °. o o • ^ - • ^ A A 9 90 o I - A ^1 _L 1 1 A 1 _L_ PH Figure 4. Oxygen affinity (log P50) and cooperativity (n5u)of Cancer anthonyi hemocyanin in the absence of calcium ions as a function of pH and temperature: 5°C (a). 25°C (•), and 35"C (O). Calcium ions were removed from the hemocyanin by dialyzing against 500 mmol/1 NaCl and 10 mmol/1 EGTA. sitive to temperature (Burnett and Infantin
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. TEMPERATURE SENSITIVITY OF HEMOCYANINS 159 5 - Cancer anthonyi £ 7> o 8#* • o <*A • * o £ • °. o o • ^ - • ^ A A 9 90 o I - A ^1 _L 1 1 A 1 _L_ PH Figure 4. Oxygen affinity (log P50) and cooperativity (n5u)of Cancer anthonyi hemocyanin in the absence of calcium ions as a function of pH and temperature: 5°C (a). 25°C (•), and 35"C (O). Calcium ions were removed from the hemocyanin by dialyzing against 500 mmol/1 NaCl and 10 mmol/1 EGTA. sitive to temperature (Burnett and Infantine 1984). The freshwater crab Holthuisana transversa has a very small Bohr shift (<) and a pronounced temperature depen- dence (Morris et 1988). However, there are also a num- ber of Hcs with large normal Bohr shifts and a convention- ally large temperature dependence as well (Jokumsen et 1981; Mauro and Mangum. 1982a, b; Bridges et al., 1983; Morris and Bridges, 1985, 1986); there must be additional selection pressures for Bohr shifts that may override the adaptive potential described here. An indirect mechanism may be responsible for the de- crease in temperature dependence at high temperatures which we have noted in some species. Andersson et al. (1982) showed that the number of available binding sites for the allosteric modulator Ca+:, which raises 02 affinity of Hcs with normal Bohr shifts, increases with tempera- ture. One might also expect an increase in Ca+2 affinity of He at high temperature due to enhanced ionic activity and possibly other factors associated with changes in pro- tein structure. We reasoned, therefore, that a greater in- teraction between calcium ions and He at higher temper- ature {, greater Ca+2 activity and more Ca+2-Hc bind- ing sites) would tend to increase oxygen affinity [provided that these Hcs respond to changes in free cal- cium ions as do those of other portunid crabs (Truchot, 1975; Mason et 1983)]
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
