Akira Hitoi

Organ-specific difference in the sugar chains of γ-glutamyltranspeptidase

Sugar chains of gamma-glutamyltranspeptidase purified from neonatal mouse liver and adult mouse kidney were quantitatively released as oligosaccharides from the polypeptide backbone by hydrazinolysis. A comparative study of the structures of the oligosaccharides has revealed that the GlcNAc beta 1 leads to 4Man beta 1 leads to group is found in the sugar chains of kidney enzyme but not in those of liver enzyme. This is considered as an organ-specific difference common to mammals because the same phenomenon was found in bovine and rat enzymes.

Sialic acid-containing sugar chains of hen ovalbumin and ovomucoid

The acidic oligosaccharide fractions released from hen ovalbumin and ovomucoid by hydrazinolysis contain both sialyloligosaccharides and sulfated oligosaccharides. The sialyloligosaccharides were converted into neutral oligosaccharides by sialidase digestion, and separated from sulfated oligosaccharides by paper electrophoresis. Structural studies of these neutral oligosaccharides showed that the oligosaccharides of ovalbumin have different structural characteristics from those of ovomucoid, i.e., all sialyloligosaccharides from ovomucoid contain a pentasaccharide, alpha-D-Manp-(1----3)-[alpha-D-Manp-(1----6)]-beta-D-Manp -(1----4)-GlcpNAc- (1----4)-GlcpNAc, as a common core, and the smallest oligomannosyl core of the sugar chains from ovalbumin is alpha-D-Manp-(1----3)-alpha-D-Manp-(1----6)-[alpha-D-Manp -(1----3)]-beta-D- Manp-(1----4)-GlcpNAc-(1----4)-GlcpNAc. By methanolysis followed by N-acetylation, sialyl oligosaccharides, free from sulfated oligosaccharides, were recovered quantitatively from the acidic fractions of ovalbumin and ovomucoid. Methylation analysis of these sialyloligosaccharide mixtures, before and after sialidase digestion, showed that all sialic acid of both glycoproteins occurs as a alpha-Sia-(2----3)-D-Galp group.

The structures of the carbohydrate moieties of mouse kidney γ-glutamyltranspeptidase: Occurrence of X-antigenic determinants and bisecting N-acetylglucosamine residues☆

Paper electrophoresis and Bio-Gel P-4 column chromatography of the oligosaccharides released from mouse kidney gamma-glutamyltranspeptidase by hydrazinolysis gave fractionation patterns quite distinct from those of the bovine and rat kidney enzymes. Structural studies of the fractionated oligosaccharides by sequential exoglycosidase digestion in combination with methylation analysis showed that mouse kidney gamma-glutamyltranspeptidase contains a series of bisected complex-type asparagine-linked sugar chains with the following oligosaccharides as their outer chain moieties: GlcNAc beta 1----, Sia alpha 2----Gal beta 1----4GlcNAc beta 1----, Gal beta 1----4(Fuc alpha 1----3)GlcNAc beta 1----, and sialylated N-acetyllactosamine repeating sugar chains. Some of these sugar chains were found for the first time in glycoproteins.

Difference in the sugar chains of two subunits and of isozymic forms of rat kidney γ-glutamyltranspeptidase

A comparative study by gel-permeation chromatographic analysis of oligosaccharides released from the heavy and the light subunits of rat kidney gamma-glutamyltranspeptidase has revealed that high-mannose-type sugar chains are found only in the heavy subunit, and the nonsialylated and nonfucosylated biantennary complex-type sugar chains are included only in the light subunit. By the same analysis of the oligosaccharide fractions obtained from four isozymic forms of rat kidney gamma-glutamyltranspeptidase, it was found that all these enzymes contain 2 mol of neutral sugar chains but different numbers of acidic sugar chains. The total numbers of sialic acid residues showed a reciprocal relationship to the isoelectric point of each isozymic form, and an increase of 1 mol of sialic acid residue corresponds to a decrease of 0.5 in the value of the isoelectric point.