A MASS-SPECTROMETRIC STUDY OF THE HETEROGENEITY OF THE MONOMER SUBUNIT OF LUMBRICUS-TERRESTRIS HEMOGLOBIN

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 subuni t, has been reported by Shishikura et al. (Biol. Chem. 1987, 262, 3123 -3131). This subunit has been found to be heterogeneous and in this st udy three fractions were separated by C-18 reverse-phase high-performa nce liquid chromatography. The major chain d(1) with molecular weight 15,993.5 +/- 2.1 u possesses S-7 instead of G(7), the partial sequence RDIIDD (33-38) instead of KGILRE, E instead of Q in positions 23 and 58, and T-84 instead of A(84). The C-terminus is K-140 instead of (DI1 42)-I-141. Chain d(3) with molecular weight 15,963.2 +/- 1.6 u showed high sequence homology with chain d(1), differing apparently only in r esidue 84 where A(84) replaces T-84. Analysis of the third chromatogra phic 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 d(2) and d(4), respectively, but their sequence assignments are not ye t certain. (C) 1997 American Society for Mass Spectrometry.