Identification of a 130-kilodalton human biliary concanavalin A binding protein as aminopeptidase N.
OBJECTIVE
Human gallbladder bile contains a group of nonmucin glycoproteins that binds to the lectin concanavalin A (con A) and has been reported to promote cholesterol monohydrate crystal nucleation, an event preceding the formation of gallstones. Several of these proteins, including a 130-kilodalton protein, have been isolated and shown to promote nucleation in vitro. The aim of this study was to identify this and other major biliary con A binding glycoproteins.


METHODS
Gallbladder bile was chromatographed on con A agarose, and the eluted proteins were electrophoresed, blotted, and subjected to amino-terminal sequence analysis.


RESULTS
The major con A binding proteins were identified as aminopeptidase N (a 130-kilodalton protein), alpha 2 macroglobulin, hemopexin, immunoglobulin heavy chains, and the beta chain of haptoglobin. After further purification, aminopeptidase N was found to be enzymatically active and to promote cholesterol crystallization at its approximate physiological concentration in bile.


CONCLUSIONS
It is likely that aminopeptidase N is the previously characterized 130-kilodalton biliary crystallization promoting protein. Aminopeptidase N is probably released from the biliary canalicular membrane by the detergent activity of bile salts and may be one factor that promotes cholesterol crystallization in the gallbladder.
Offner
G D
GD
Department of Medicine, Boston University School of Medicine, Massachusetts.
Gong
D
D
Afdhal
N H
NH
D000595:Amino Acid Sequence; D000626:Aminopeptidases / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D001646:Bile / Q000378:metabolism*; D018826:CD13 Antigens; D002784:Cholesterol / Q000502:physiology; D003208:Concanavalin A / Q000378:metabolism*; D003460:Crystallization; D005704:Gallbladder / Q000201:enzymology; D006023:Glycoproteins / Q000378:metabolism*; D006801:Humans; D007120:Immunochemistry; D008970:Molecular Weight; D009994:Osmolar Concentration
D006023:Glycoproteins; D003208:Concanavalin A; D002784:Cholesterol; D000626:Aminopeptidases; D018826:CD13 Antigens