Substrate specificity of endo-β-galactosidases from Flavobacterium keratolyticus and Escherichia freundii is different from that of Pseudomonas sp

The substrate specificity of endo-β-galactosidase of Pseudomonas sp. was found to differ from that of Flavobacterium keratolyticus or Escherichia freundii, based on the following experimental results. (a) The endo-β-galactosidases from these three bacteria released 6-O-sulfo-GlcNAcβ1-3Gal as one of the major products from keratan sulfates from different sources. In addition to the sulfated disaccharide, Flavobacterium and Escherichia enzymes produced GlcNAcβ1-3Gal, which is also an integral repeating unit of keratan sulfate, whereas the Pseudomonas enzyme did not release any non-sulfated disaccharide. (b) Tetrasaccharides were prepared from the teleost skin keratan sulfate by digestion with Pseudomonas enzyme followed by gel filtration on Sephadex G-50 chromatography. A part of the tetrasaccharide fraction was hydrolyzed by Flavobacterium enzyme to produce 6-O-sulfo-GlcNAcβ1- 3Gal and GlcNAcβ1-3Gal, whereas the fraction was completely resistant to retreatment with the Pseudomonas enzyme. (c) Endo-β-galactosidases from F. keratolyticus and E. freundii hydrolyzed the internal β-1,4-galactosyl linkage of various neolacto-type glycosphingolipids to produce glucosylceramides. However, these glycosphingolipids were completely resistant to the Pseudomonos enzyme. These findings clearly show that the sulfation on the N-acetylglucosamine adjacent to galactose in the lactosaminoglycans is essential for expression of the Pseudomonas enzyme, but not for that of the Flavobacterium or Escherichia enzyme.