The half-saturation value, P50, for 'stripped' hemoglobins from Trematomus spp. (fam. Nototheniidae) at pH 8.27 and -1.8 degrees C varied from 12.1 mmHg in the pelagic species T. borchgrevinki to 1.3 mmHg in the sedentary benthic species T. centronotus. 2. The nototheniid hemoglobins showed appreciable Bohr effects (phi = delta log P50/delta pH = -0.87 to -0.48) while the hemoglobin from a bathydraconid species, Gymnodraco acuticeps, was insensitive to pH; phi = -0.02 No Root shifts were detected. 3. Cooperative oxygen binding was present in all hemoglobins with Hill's coefficient, n, ranging from 1.21 +/- 0.14 in Dissostichus mawsoni to 2.28 +/- 0.88 in T. borchgrevinki among the Nototheniidae, and n = 1.50 +/- 0.14 in G. acuticeps. 4. A small increase in P50- was promoted by ATP for hemoglobins from T. borchgrevinki, T. bernacchii and D. mawsoni but significant temperature effects on oxygen binding were manifested, with apparent heats of oxygenation, delta H, = -56.13, 62.16, and -23.98 kJ mol-1, respectively.
