The biosynthesis of crustacean chitin. Isolation and characterization of polyprenol-linked intermediates from brine shrimp microsomes

Abstract

The biosynthesis of crustacean chitin appears to involve the participation of a lipid-linked intermediate. A microsomal preparation from larval stages of the brine shrimp Artemia salina was found to catalyze the glycosylation of exogenous [ 3H]dolichol phosphate, yielding a product which was insoluble in chloroform:methanol (2:1) but soluble in chloroform:methanol:water (10:10:3). Artemia microsomes catalyze the transfer of N-acetylglucosamine from UDP- N-acetylglucosamine to a lipid acceptor. After extraction of labeled lipids with either chloroform:methanol (2:1) or chloroform:methanol:water (10:10:3), labeled compounds could be purified by ion-exchange chromatography on DEAE-Sephacel. Mild acid hydrolysis of 3H- N-acetylglucosamine labeled material soluble in chloroform:methanol:water (10:10:3) yielded a series of oligosaccharides ranging from 2 to about 8 glycosyl units in size. The larger components were shown to be sensitive to chitinase digestion but resistant to treatment with α-mannosidase. Such 3H- N-acetylglucosamine containing compounds, prepared by both in vivo and in vitro procedures, appear to be chitin oligosaccharides. Brine shrimp microsomes also catalyze the transfer of mannose from GDP-mannose to a lipid acceptor. Mild acid hydrolysis of mannosyl lipids soluble in chloroform:methanol:water (10:10:3) yielded oligosaccharides which were sensitive to α-mannosidase digestion and resistant to treatment with endochitinase. The results suggest 3H- N-acetylglucosamine-labeled oligosaccharide-lipids are distinct from the mannose-labeled fraction and may participate in the formation of an endogenous primer for chitin synthesis after their transfer to a protein acceptor.