Amino acid sequence around the thiolester of α2‐macroglobulin from plasma of the crayfish, Pacifastacus leniusculus

Abstract
α2-Macroglobulin (α2M) was isolated from plasma of the freshwater crayfish, Pacifastacus leniusculus, using ultracentrifugation, ion-exchange chromatography and gel filtration techniques. The Pacifastacus α2M molecule (Pα2M) was radioactively labeled in the thiol ester structure with iodo [14C]acetic acid in the presence of methylamine. After reduction and carboxymethylation of the protein, it was digested with trypsin. A 14C-labeled tryptic peptide was sequenced and contained an amino acid sequence very similar to other known thiol ester sequences from human α2M and related proteins. The N-terminal sequence of Pα2M was related to that recently determined for lobster α2M [(1987) J. Biol. Chem. 262, 14606–14611].