Isolation of peptides homologous to domains of human α 1B-glycoprotein from a mongoose antihemorrhagic factor

Thirteen peptides, homologous to one of the five domains of human alpha 1B-glycoprotein (alpha 1BG), were isolated from a mongoose antihemorrhagic factor (AHF1); four of them were generated by BrCN cleavage, and three and six peptides by the digestions with lysyl endopeptidase and staphylococcal protease V8, respectively. The purified peptides covered 75.9% of the whole sequence of human alpha 1BG (359/474 residues) and showed 46.4% identity (167/360 amino acids) with the sequence of human alpha 1BG including cysteine residues forming disulfide linkages. One of the sugar binding sites of human alpha 1BG was also conserved in AHF1. These results suggest that AHF1 is a protein homologous to human alpha 1BG and a supergene family of immunoglobulins.