Chris Astall

A comparative study of the oxygen transporting properties of the haemocyanin of five species of thalassinidean mud-shrimps

Comparative studies of the haemocyanin of five species of thalassinidean mud-shrimps showed that all five species exhibited a high oxygen affinity (P50 range=1.0–9.3 Torr, at in vivo pH, 10°C). Each of the mud-shrimps exhibited a moderately large Bohr coefficient (−1.06 to −1.48) and values for the co-operativity of the haemocyanin did not differ greatly between the species (n50 range=2.3–3.8). The highest oxygen affinities were recorded for the haemocyanin of Callianassa subterranea, Jaxea nocturna and Calocaris macandreae, whereas those for the two species of Upogebia were slightly lower but were still higher than in many other decapods. The higher oxygen affinity of the haemocyanin of the deposit feeding shrimps C. subterranea, J. nocturna and C. macandreae compared with that of the haemocyanin of the filter feeding upogebiids may be correlated with the fact that conditions within the burrows of the deposit feeders may be more severely hypoxic. The oxygen affinity of all five species showed a moderate temperate sensitivity (ΔH −56.8 to −82.1 kJ mol−1 over temperature range 5–10°C). Studies of the haemocyanin of one species (C. macandreae) showed that L-lactate did not affect the oxygen affinity of the haemocyanin as has been reported for a number of other decapod species. The oxygen carrying capacity of the haemocyanin (CHCYO2) was similar in four of the species studied (0.22–0.42 mmol l−1) but that of C. subterranea was significantly greater (0.83 mmol l−1). The higher protein concentration of the haemolymph of this species also resulted in the haemolymph having a greater buffering capacity (−7.67 mmol l−1 pH unit−1). SDS–PAGE studies of the haemocyanin demonstrated the presence of 3 subunits in the upogebiids but additional subunits were observed in the other species (MW range=70 000–90 000 Da). Studies of the association state of the haemocyanin of three of the species showed that the haemocyanin of both C. macandreae and J. nocturna was present mainly in the form of eikositetramers (24-subunit aggregation state) with some hexameric haemocyanin also occurring. The haemocyanin of Upogebia deltaura, however, occurred as a mixture or eikositetramers and dodecamers.

Preservice High School Science Teacher Identity

The construct of teacher identity is complex and difficult to define. In addition to professional elements such as subject knowledge, teaching skills and understanding of pedagogical practices, it encompasses personal ideas about what teachers are and what they are expected to be. Sachs (2005) has described teacher identity quite succinctly as a framework for teachers to construct their own ideas of “how to be”, “how to act” and “how to understand” their work and their place in society.