Limulus α2-macroglobulin. First evidence in an invertebrate for a protein containing an internal thiol ester bond

摘要: Intra-chain thiol ester bonds are present in a limited number of proteins. The class proteins includes vertebrate alpha 2-macroglobulin and the complement C3 C4. We report here first instance protein from an invertebrate, proteinase-inhibitor homologue plasma American horseshoe crab Limulus polyphemus. Our evidence is three kinds: (1) proteinase-binding activity inactivated by low-molecular-mass primary amine methylamine; (2) native subject to autolytic fragmentation during mild thermal denaturation, yielding fragments approx. 125 kDa 55 kDa, whereas methylamine-treated stable under these conditions treatment; (3) new groups generated rapidly reaction with trypsin. demonstration bond ancient invertebrate provides evolutionary for importance this function forms 2-macroglobulin-like proteinase inhibitors.