MULTIPLE NONREDUCING CHAIN TERMINI ISOLATED FROM BOVINE CORNEAL KERATAN SULFATES

Keratan sulfate-containing proteoglycans were isolated from bovine cor nea (15-month old to 3-year-old animals) and digested with the enzyme, keratanase II. The released oligosaccharides, which included non-redu cing termini and repeat region oligosaccharides but not linkage region s, were reduced with alkaline borohydride and fractionated on a Spheri sorb column, These oligosaccharides were examined by 600-MHz H-1 NMR s pectroscopy using one- and two-dimensional methods and, in addition to some oligosaccharide alditols previously recovered from skeletal kera tan sulfate, the following new capping structures were identified: Neu Ac alpha 2-6Gal beta 1-4GlcNAc(S)-ol, NeuAc alpha 2-3Gal(S)beta 1-4-Gl cNAc(S)beta 1-3Gal beta 1-4GlcNAc(S)-ol, NeuGc alpha 2-6Gal beta 1-4Gl cNAc(S)beta 1-3Gal beta 1-4GlcNAc(S)-ol, NeuGc alpha 2-3Gal beta 1-4Gl cNAc(S)beta 1-3Gal beta 1-4GlcNAc(S)-ol, NeuGc alpha 2-3Gal-(S)beta 1- 4GlcNAc(S)beta 1-3Gal beta 1-4GlcNAc(S)-ol, NeuGc alpha 2-3Gal-(S)beta 1-4GlcNAc(S)beta 1-3Gal(S)beta 1-4GlcNAc(S)-ol, Gal alpha 1-3Gal beta 1-4GlcNAc(S)beta 1-3Gal beta 1-4GlcNAc(S)-ol,Gal alpha 1-3Gal beta 1- 4GlcNAc(S)beta 1-3Gal(S)beta 1-4GlcNAc(S)-ol, GlcNAc(S)beta 1-3Gal(S)b eta 1-4GlcNAc(S)-ol, and GalNAc(S)-beta 1-3Gal(S)beta 1-4GlcNAc(S)-ol. These structures represent seven families of capping residues, whose relative molar proportions are given in parentheses: NeuAc alpha(2-3)- (12%), NeuAc alpha(2-6)- (41%), NeuGc alpha(2-3)- and NeuGc alpha(2-6 )- families (12%), Gal alpha(1-3)- (26%), GalNAc(S)beta(1-3)- (5%), an d GlcNAc(S)beta(1-3)(4%), It is not clear, at present, where each of t hese structures occurs on the bi-antennary N-linked corneal keratan su lfate chains, which themselves occur within three keratan sulfate prot eoglycan species. However, examination of the relative proportions of the capping to the repeat structures and knowledge of the average mole cular size suggests that the sum of these non-reducing termini represe nts the caps of two antennae.