Isolation and properties of two sialate-O-acetylesterases from horse liver with 4- and 9-O-acetyl specificities.
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 (K(M) 1.1 mM), while that with the higher pI esterifies both 4- and 9-O-acetylated monosaccharides at similar rates (K(M) 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.
Schauer
Roland
R
Biochemisches Institut, Christian-Albrechts-Universität, Olshausenstr. Kiel, Germany. schauer@biochem.uni-kiel.de
Shukla
Ashok K
AK
D000107:Acetylation; D000115:Acetylesterase; D000818:Animals; D002265:Carboxylic Ester Hydrolases / Q000302:isolation & purification* / Q000378:metabolism*; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D006736:Horses; D007525:Isoelectric Focusing; D008099:Liver / Q000201:enzymology*; D008970:Molecular Weight; D013379:Substrate Specificity
D002265:Carboxylic Ester Hydrolases; D000115:Acetylesterase; C046298:sialate O-acetylesterase