Oxygen-binding characteristics of three extra-cellular haemoglobins of Artemia salina

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Abstract
The O2-binding characteristics of the 3 extracellular Hb of brine shrimp (A. salina) were studied in vitro by using highly purified preparations. Hb I is induced last in the development of brine shrimps when functional gills are formed. It has the lowest O2 affinity (p50 [median partial pressure of O2] 5.34 mmHg), an intermediate Bohr effect (.vphi. -0.09 at 20.degree. C) above pH 8 and a temperature-sensitivity (.DELTA.H -44.8 to -45.6 kJ/mol at pH 8-9) comparable with those observed with other invertebrate Hb [Weber et Heidemann 1977]. Hb II, the 1st induced (soon after hatching of nauplius larvae) persists generally throughout adult life. It has an intermediate O2 affinity (p50 3.7 mmHg), the highest Bohr effect (.vphi. 0.21 at 20.degree. C) above pH 8 and a similar temperature-sensitivity (.DELTA.H -46.0 to -54.8 kJ/mol at pH 8-9) as Hb I. Hb III, which is induced next, several hours after the induction of Hb II, but disappears from the hemolymph in the middle of adult life, has the highest O2 affinity (p50 1.8 mmHg), the lowest Bohr effect (.vphi. -0.03 at 20.degree. C) above pH 8.5 and a high resistance against temperature variation between 10.degree.-25.degree. C at pH 8.5-9 (.DELTA.H -22.6 to -23.0 kJ/mol). At pH 7.5-8, Hb III exhibits a similar temperature-sensitivity under 30.degree. C as other Hb. All 3 Hb have a rather low co-operativity, with Hill coefficients (h 1.6-1.9 at pH 8.5), dependent on both pH and temperature. The highest co-operativity was seen at 20.degree. C and pH 9 for Hb I and II, whereas it was at 27.degree. C and pH 8.5 for Hb III. The O2-binding behavior of Hb III in vitro is significantly different from those of Hb I and II and indicates possibly its specific physiological role in vivo in the adaptive process in the natural environment.