Amino acid sequence of the N-terminus and selected tryptic peptides of the active subunit of human plasma carboxypeptidase N: comparison with other carboxypeptidases.
Human plasma carboxypeptidase N was purified to homogeneity and its active and inactive subunits were separated. By introducing a novel technique, both forms of the active subunit (Mr = 55,000 and Mr = 48,000) were isolated. N-terminal sequencing of the active subunit of human carboxypeptidase N revealed significant homology with the N-terminal sequence of bovine carboxypeptidase H (43% identity) and to a lesser extent with carboxypeptidase A (29% identity) or carboxypeptidase B (18% identity). The active subunit of carboxypeptidase N was hydrolyzed with trypsin and 4 of the tryptic peptides were isolated by HPLC and sequenced. The sequences of the four peptides were homologous (39-64% identity) with regions of carboxypeptidase H corresponding to the middle (residues 148-175) and C-terminal portion (residues 321-408). These regions had essentially no homology with carboxypeptidase A or B. These data indicate that carboxypeptidase H and the active subunit of carboxypeptidase N may have diverged from a common ancestral gene.
Skidgel
R A
RA
Department of Anesthesiology, University of Illinois, Chicago College of Medicine 60612.
Bennett
C D
CD
Schilling
J W
JW
Tan
F L
FL
Weerasinghe
D K
DK
Erdös
E G
EG
D000595:Amino Acid Sequence; D002268:Carboxypeptidases / Q000097:blood / Q000302:isolation & purification; D006801:Humans; D001121:Lysine Carboxypeptidase / Q000097:blood / Q000302:isolation & purification; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010446:Peptide Fragments / Q000032:analysis; D014357:Trypsin
D046911:Macromolecular Substances; D010446:Peptide Fragments; D002268:Carboxypeptidases; D001121:Lysine Carboxypeptidase; D014357:Trypsin