THE MULTI-HEMOGLOBIN SYSTEM OF THE HYDROTHERMAL VENT TUBE WORM RIFTIA-PACHYPTILA .1. REEXAMINATION OF THE NUMBER AND MASSES OF ITS CONSTITUENTS

The deep-sea tube worm Riftia pachyptila Jones possesses a well develo ped circulatory system and a large coelomic compartment, both containi ng extracellular hemoglobins, Fresh vascular blood is heterogeneous an d contains two different hemoglobins (V1 and V2), whereas the coelomic fluid is homogeneous and comprises only one hemoglobin (C1), Their mo lecular weights have been determined by scanning transmission electron microscopy mass mapping (STEM) and by multi-angle laser light scatter ing (MALLS). Both methods yielded approximately the same molecular wei ghts with masses significantly higher than the literature data for V1, V1, V2, and C1 had M(r) of 3396 +/- 540 x 10(3), 393 +/- 71 x 10(3), and 410 +/- 51 x 10(3) by STEM, and 3503 +/- 13 x 10(3), 433 +/- 8 x 1 0(3), and 380 +/- 4 x 10(3) by MALLS, respectively, Transmission elect ron micrographs of V1 are typical of an hexagonal bilayer hemoglobin ( HBL Hb), When submitted to dilution or osmotic shock, V1 dissociates i nto halves and one-twelfth subunits like annelid HBL Hbs, V1 is resist ant to urea treatment, indicating that hydrophobic interactions play a small role in its quaternary structure, Conversely, V1 Hb is rather u nstable in solution without denaturant, a property which seems to be c haracteristic of vestimentiferan HBL Hbs and could be explained by an important number of hydrogen bonds.