SEQUENCE SIMILARITY BETWEEN ALPHA-2-MACROGLOBULIN FROM THE HORSESHOE-CRAB, LIMULUS-POLYPHEMUS, AND PROTEINS OF THE ALPHA-2-MACROGLOBULIN FAMILY FROM MAMMALS

1. 1. Purified α2-macroglobulin (α2M) from the American horseshoe crab, Limulus polyphemus was cleaved with trypsin and 20 of the tryptic peptides were sequenced and compared with the sequences of human α2M, rat α1M, α2M, and α1-inhibitor 3, and human complement proteins C3 and C4. 2. 2. Ten of the peptides (233 residues), including that containing the thiol ester site, could be aligned unambiguously with stretches in mammalian α2M, with a degree of identity greater than 30%. 3. 3. The 12-residue thiol ester-containing peptide of Limulus α2M showed 67% identity with the same stretch of human α2M. © 1990.