Hemoglobins of two terebellid polychaetes: Enoplobranchus sanguineus and Amphitrite ornata
1. 1. The intracellular, coelomic hemoglobins of the terebellid annelids Enoplobranchus sanguineus and Amphitrite ornata are momoneric proteins possessing high O2 affinities (half-saturation O2 tension, P50 = 1.4 and 2.8 mm, respectively, at 20°C), and lacking homotropic or heterotropic interactions in O2 binding. These O2 affinities are high relative to extracellular vascular hemoglobins, but low relative to mammalian myoglobins, due to considerably higher rates of O2 dissociation. 2. 2. The extracellular, multi-subunit hemoglobin (erythrocruorin) from the vascular system of A. ornata has a low O2 affinity (P50 about 11 mm Hg at 20°C) and shows significant heme-heme interaction (Hill's constant n50 = 1.5-2.0). It lacks a Bohr effect between pH 5.8 and 8.0, but shows a large increase in O2 affinity above pH 8.0 that may be due to dissociation into high affinity subunits. 3. 3. The amino acid composition and the amino acid sequence for the first 29 residues of intracellular E. sanguineus hemoglobin show a surprising lack of homology with other simple heme proteins. © 1977.
Weber, RE; Mangum, C; Steinman, H; Bonaventura, C; Sullivan, B; Bonaventura, J
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