STRUCTURAL FEATURES OF GLYCERA-DIBRANCHIATA MONOMER HEMOGLOBINS - PRIMARY SEQUENCES OF MONOMER HEMOGLOBIN COMPONENT-II AND COMPONENT-III

Primary sequences for the remaining two members (GMH2, GMH3) of the gr oup of three major monomeric hemoglobins from the marine annelid Glyce ra dibranchiata have been obtained. Full sequences of each 147-amino a cid globin were achieved with a high degree of confidence using standa rd Edman technology in combination with molecular mass determinations of the intact globins and of the cyanogen bromide cleavage fragments u sing electrospray ionization mass spectrometry. When minor assumptions concerning Q/E identities are made these new results indicate the lik ely correspondence of GMG2 with the protein represented by the first G lycera dibranchiata monomer hemoglobin complete sequence [Imamura et a l., (1972), J. Biol. Chem. 247, 2785-2797]. When these new sequences a re combined with the previously determined primary sequence for the th ird major monomer hemoglobin, GMH4 [Alam et al., J. Protein Chem. (199 4), 13, 151-164], it becomes clear that these three (GMG2-4) are truly distinct proteins, contrary to previous suggestions. Surprisingly, ou r results show that none of these three primary sequences is identical to the published sequence of the refined monomer hemoglobin crystal s tructure protein; however, there is a strong correspondence to the GMG 2 sequence. The present sequencing results, in combination with the pu blished GMH4 sequence, confirm the presence of a distal Leu in place o f the more commonly encountered distal His in all three of the major m onomer hemoglobins isolated in this laboratory and indicate that the u nusual B10 Phe occurs only in GMH4. Analysis of the sequences presente d here, along with comparison of amino acid content for Glycera dibran chiata monomer hemoglobins isolated from three different laboratories, and comparison of NMR results from two laboratories suggest further c orrespondences which unify disparate published isolations.