Oxygen Binding in Artemia Hemolymph
Two Artemia species, i.e. Great Salt Lake (A. franciscana) and Kazakhstan (A. parthenogenetica) were submitted to a stepwise lowering of the partial oxygen pressure until 1 ml 02.L−1 was reached in the saline medium (35%). The increase of hypoxia resulted in the increase of the hemoglobin concentration of the hemolymph. Oxygen binding was determined in small freshly collected hemolymph samples (2 to 4 ul) of preadult females. The oxygen binding curves show an undulating biphasic course. This phenomenon only occurs with Artemia hemolymph and was never noticed when measuring Artemia hemoglobin extracts. Similar curves have been reported [1,2] for the vertebrate sickle cell Hbs, which are sensitive to aggregation, gelation and crystallization effects resulting in biphasic oxygen binding curves. As far as we know, this is the first time that biphasic oxygen binding curves have been registrated for blood solutions containing invertebrate Hbs. Our results reveal that both Artemia species show biphasic oxygen binding curves for hemolymph with and without buffer (pH 8.58) and/or added GTP (3.1 mg.mL−1). Oxygen affinity (p50) and cooperativity (n50) were also determined (25°C).