A Role For Ca2+ in the Thermal and Urea Denaturation of Haemocyanin from Aestivating Giant African Snails Achatina achatina
Abstract
Giant African snail (Achatina achatina) becomes dormant (aestivate) under harsh environmental conditions like dry seasons. During this period the animal accumulates urea and is faced with thermal death. The stability towards thermal and urea denaturation of haemocyanin from aestivating and nonaestivating A. achatina has been investigated using UV spectroscopy.Thermodynamic parameters calculated show a complex process with two sets of activation energy (Ea); 4.64kcal/mol, 14.39kcal/mol for nonaestivating and 5.77kcal/mol, 17.66kcal/mol for aestivating snails. With aestivating snails having a higher melting temperature 70oC, compared to 60oC for nonaestivating snails. The results also indicate that calcium concentration is increased during aestivation and this increase is responsible for the high conformational stability (ΔGoH2O) of haemocyanin from aestivating snails that is 1.8kcal/mol for nonaestivating and 1.5kcal/mol for aestivating snails in the absence of Ca2+ as against 1.9kcal/mol and 2.0kcal/mol for nonaestivating snails in the absence of Ca2+ as against 1.9kcal/mol and 2.0kcal/mol for nonaestivating and aestivating snails respectively in the presence of 15nM Ca2+. Thus Ca2+ plays an important role in the stability of haemocyanin during aestivation.
Key Words: Snails, Achatina achatina, haemocyanin, aestivation, thermal and urea denaturation, thermostability and conformational stability.
Bio-Research Vol.2(2) 2004: 54-62
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