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
V. Kaartinen et al., 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, The Journal of biological chemistry, 267(10), 1992, pp. 6855-6858
Human glycoasparaginase (N4-(beta-N-acetyl-D-glucosaminyl)-L-asparagin
ase, EC 3.5.1.26) hydrolyzes a series of compounds that contain L-aspa
ragine residue with free alpha-amino and alpha-carboxyl groups. Substr
ates include high mannose and complex type glycoasparagines as well as
those that lack the di-N-acetylchitobiose moiety, L-aspartic acid bet
a-methyl ester and L-aspartic acid beta-hydroxamate. The enzyme is ina
ctive toward L-asparagine and L-glutamine and glycoasparagines contain
ing substituted alpha-amino and/or alpha-carboxyl groups. In the prese
nce of the acyl acceptor hydroxylamine, glycoasparaginase catalyzes th
e synthesis of L-aspartic acid beta-hydroxamate from aspartyl-glucosam
ine, L-aspartic acid beta-methyl ester, and L-aspartic acid. C-13 NMR
studies using O-18-labeled L-aspartic acid demonstrate that glycoaspar
aginase catalyzes an oxygen exchange between water and the carboxyl gr
oup at C-4 of L-aspartic acid. These results indicate that glycoaspara
ginase reacts as an exo-hydrolase toward the L-asparagine moiety of th
e substrates and the free alpha-amino and alpha-carboxyl groups are re
quired for the enzyme reaction. The results are consistent with an L-a
sparaginase-like reaction pathway which involves a beta-aspartyl enzym
e intermediate. Since glycoasparaginase is active toward a series of s
tructurally different glycoasparagines, we suggest the revised systema
tic name of N4-(beta-glycosyl)-L-asparaginase for the enzyme.