Substrate specificity and reaction mechanism of human glycoasparaginase. The N-glycosidic linkage of various glycoasparagines is cleaved through a reaction mechanism similar to L-asparaginase.
Human glycoasparaginase (N4-(beta-N-acetyl-D-glucosaminyl)-L-asparaginase, EC 3.5.1.26) hydrolyzes a series of compounds that contain L-asparagine residue with free alpha-amino and alpha-carboxyl groups. Substrates include high mannose and complex type glycoasparagines as well as those that lack the di-N-acetylchitobiose moiety, L-aspartic acid beta-methyl ester and L-aspartic acid beta-hydroxamate. The enzyme is inactive toward L-asparagine and L-glutamine and glycoasparagines containing substituted alpha-amino and/or alpha-carboxyl groups. In the presence of the acyl acceptor hydroxylamine, glycoasparaginase catalyzes the synthesis of L-aspartic acid beta-hydroxamate from aspartyl-glucosamine, L-aspartic acid beta-methyl ester, and L-aspartic acid. 13C NMR studies using 18O-labeled L-aspartic acid demonstrate that glycoasparaginase catalyzes an oxygen exchange between water and the carboxyl group at C-4 of L-aspartic acid. These results indicate that glycoasparaginase reacts as an exo-hydrolase toward the L-asparagine moiety of the substrates and the free alpha-amino and alpha-carboxyl groups are required for the enzyme reaction. The results are consistent with an L-asparaginase-like reaction pathway which involves a beta-aspartyl enzyme intermediate. Since glycoasparaginase is active toward a series of structurally different glycoasparagines, we suggest the revised systematic name of N4-(beta-glycosyl)-L-asparaginase for the enzyme.
Kaartinen
V
V
Department of Clinical Chemistry, Kuopio University Central Hospital, Finland.
Mononen
T
T
Laatikainen
R
R
Mononen
I
I
D000596:Amino Acids / Q000378:metabolism; D001227:Aspartylglucosylaminase / Q000378:metabolism*; D002384:Catalysis; D006020:Glycopeptides / Q000378:metabolism*; D006027:Glycosides / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D013379:Substrate Specificity
D000596:Amino Acids; D006020:Glycopeptides; D006027:Glycosides; C007872:glycoasparagines; D001227:Aspartylglucosylaminase