A mass spectrometric study of the heterogeneity of the monomer subunit of Lumbricus terrestris hemoglobin

Abstract

The subunits of the hemoglobin of Lumbricus terrestris consist of heme-binding globin chains, designated a, b, c, and d, and linker chains. The sequence of chain d, which is also referred to as a monomer subunit, has been reported by Shishikura et al. (Biol. Chem.1987, 262, 3123–3131). This subunit has been found to be heterogeneous and in this study three fractions were separated by C18 reverse-phase high-performance liquid chromatography. The major chain d1 with molecular weight 15,993. 5 ± 2. 1 u possesses S7 instead of G7, the partial sequence RDIIDD (33–38) instead of KGILRE, E instead of Q in positions 23 and 58, and T84 instead of A84. The C-terminus is K140 instead of D141I142. Chain d3 with molecular weight 15,963. 2 ± 1. 6 u showed high sequence homology with chain d1, differing apparently only in residue 84 where A84 replaces T84. Analysis of the third chromatographie fraction revealed two additional chains with molecular weights of 15,996. 1 ± 1. 4 and 15,937. 6 ± 1. 2 u. These are designated chains d2 and d4, respectively, but their sequence assignments are not yet certain.