Isolation and properties of two sialate-<Emphasis Type="Italic">O</Emphasis>-acetylesterases from horse liver with 4- and 9-<Emphasis Type="Italic">O</Emphasis>-acetyl specificities |
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Authors: | Roland Schauer Ashok K Shukla |
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Institution: | 1.Biochemisches Institut,Christian-Albrechts-Universit?t,Kiel,Germany;2.Glygen Corp.,Columbia,USA |
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Abstract: | Sialate-O-acetylesterase was purified almost 900-fold from particle-free supernatants of horse liver by gel filtration, ion-exchange
chromatography and isoelectric focussing. The native enzyme on gel filtration exhibits a molecular weight of 54,000 Da. It
was separated by isoelectric focussing into two forms with pI values of 4.8 and 5.7, respectively. The esterase with a lower pI hydrolyses only 9-O-acetyl groups from sialic acids (KM 1.1 mM), while that with the higher pI esterifies both 4- and 9-O-acetylated monosaccharides at similar rates (KM 0.3 M and 1.3 mM, respectively). Both forms are inactive with 7-O-acetylated N-acetylneuraminic acid. Enzyme assays were carried out at the pH optimum (pH 8.4–8.6) using free O-acetylated sialic acids followed by direct analysis of the reaction products by isocratic anion-exchange HPLC. Glycosidically
bound sialic acids can also be de-O-acetylated. Horse liver esterase seems to be an essential enzyme for the catabolism of 4-O-acetylated sialoglycoconjugates, since sialidase from this tissue cannot act on 4-O-acetylated sialic acids. |
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Keywords: | Sialic acid 4-O-acetylated sialic acid 9-O-acetylated sialic acid Sialate esterase Isolation and properties Horse liver |
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