Characterization and functional properties of the extracellular coelomic hemoglobins from the deep-sea, hydrothermal vent scaleworm Branchipolynoe symmytilida

Polychaete species belonging to the genus Branchipolynoe are commensal with mussels from deep-sea hydrothermal vents and cold-seeps. Possessing hemogl obins (Hbs), the species B. symmytilida, which is found in the mussel Bathy modiolus thermophilus on the East Pacific Rise, is exceptional in a family normally devoid of respiratory pigments. In a previous paper(1) we describe d two major coelomic extracellular hemoglobins with unique quaternary struc tures. Aiming to discern respiratory adaptations to the highly variable hyd rothermal environment, this paper characterizes the functional properties o f these Hbs and the coelomic fluid. The two major hemoglobins (C1 and C2) e xhibit spectrophotometric characteristics of both intra- and extracellular hemoglobins, However, their amino acid content is very different from other known hemoglobins and is characterized by a high proportion of alanine and glycine (up to 40% cumulated in C1), C1 and C2 differ markedly by their cy steine content (0.8% and 13% respectively). The coelomic fluid exhibits a s trong buffer capacity due to the high hemoglobin content (3 mM heme), In vi tro, CO2 accumulation (up to 10-12 mM CO2 for P-CO2 = 7.5 Torr) occurs with limited pH changes and is only partly accounted for by carbamino-Hb format ion. The two hemoglobins exhibit high oxygen-affinities (P-50 0.4 Torr for C1 and 0.9 Torr for C2, at 10 degrees C, pH 8) and a normal Bohr effect (Ph i values ranging from -0.54 and -0.37 at 10 degrees C, to -0.24 and -0.28 a t 30 degrees C, for C1 and C2, respectively), Cooperativity values range fr om 0.8 to 1.9 for C1 and from 0.8 to 1.7 for C2, The temperature sensitivit y of O-2 affinity reflect Delta H values that decrease from -30 to -60 kJ m ol(-1) with increasing pH, C2 exhibits a slight specific effect of CO2 on o xygenation properties. Proteins 1999; 34:435-442. (C) 1999 Wiley-Liss, Inc.