PT  - JOURNAL ARTICLE
AU  - SIDNEY SHIFRIN
AU  - BARBARA G. SOLIS
TI  - Reaction of <em>N</em>-Acetylimidazole with L-Asparaginase
DP  - 1972 Sep 01
TA  - Molecular Pharmacology
PG  - 561--564
VI  - 8
IP  - 5
4099  - http://molpharm.aspetjournals.org/content/8/5/561.short
4100  - http://molpharm.aspetjournals.org/content/8/5/561.full
SO  - Mol Pharmacol1972 Sep 01; 8
AB  - L-Asparaginase from Escherichia coli B was treated with N-acetylimidazole over a wide range of concentrations. The results indicate that the 44 tyrosyl residues of native asparaginase can be divided into three classes. The first group consists of 5-7 tyrosyl residues that react readily with the reagent and are not involved in the catalytic site. The second class consists of 10-12 aromatic residues that react less rapidly with acetylimidazole and whose modification results in a 70% decrease in enzyme activity. Full activity can be restored after deacetylation with hydroxylamine. The third class consists of the remaining tyrosyl groups that are unavailable for acetylation in the native enzyme. All the tyrosyl residues could be acetylated in 8 M urea. Modification of 10 residues in urea did not interfere with subunit reassociation, with acetylation of 15-22 residues gave variable results. Modification of 30-44 residues interfered with reassociation of the subunits. Removal of the acetyl groups with hydroxylamine, however, did not allow the subunits to aggregate, because of other, irreversible reaction of acetylimidazole with the denatured protein.