THE MULTI-HEMOGLOBIN SYSTEM OF THE HYDROTHERMAL VENT TUBE WORM RIFTIA-PACHYPTILA .2. COMPLETE POLYPEPTIDE-CHAIN COMPOSITION INVESTIGATED BYMAXIMUM-ENTROPY ANALYSIS OF MASS-SPECTRA

The deep-sea tube worm Riftia pachyptila Jones possesses a complex of three extracellular Hbs: two in the vascular compartment, V1 (similar to 3500 kDa) and V2 (similar to 400 kDa), and one in the coelomic cavi ty, C1 (similar to 400 kDa). These native Hbs, their dissociation prod ucts and derivatives were subjected to electrospray ionization mass sp ectrometry (ESI-MS). The data were analyzed by the maximum entropy dec onvolution system. We identified three groups of peaks for V1 Hb, at s imilar to 16, 23-27, and 30 kDa, corresponding to (i) two monomeric gl obin chains, b (M(r) 16,133.5) and c (M(r) 16,805.9); (ii) four linker subunits, L1-L4 (M(r) 23,505.2, 23,851.4, 26,342.4, and 27,425.8, res pectively); and (iii) one disulfide-bonded dimer D1 (M(r) 31,720.7) co mposed of globin chains d (M(r) 15,578.5) and e (M(r) 16,148.3), V2 an d C1 Hbs had no linkers and contained a glycosylated monomeric globin chain, a (M(r) 15,933.4) and a second dimer D2 (M(r) 32,511.7) compose d of chains e and f (M(r) 16,368.1). The dimer D1 was absent from C1 H b, clearly differentiating V2 and C1 Hbs. These Hbs were also subjecte d to SDS-PAGE analysis for comparative purposes, The following models are proposed ((cD1)(bD1)(3)) for the one-twelfth protomer of V1 Hb, (( cD)(bD)(6)(aD)) (D corresponding to either D1 or D2) for V2 and C1 Hbs . HBL V1 Hb would be composed of 180 polypeptide chains with 144 globi n chains and 36 linker chains, each twelfth being in contact with thre e linker subunits, providing a total molecular mass = 3285 kDa. V2 and C1 would be composed of 24 globin chains providing a total molecular mass = 403 kDa and 406 kDa, respectively. These results are in excelle nt agreement with experimental M(r) determined by STEM mass mapping an d MALLS (8).