Internal localization of nucleoside-catabolic enzymes in Escherichia coli.

Abstract

When subjected to osmotic shock, cells of E. coli release various enzymes participating in nucleoside catabolism. These enzymes include uridine phosphorylase [EC 2.4.2.3], (deoxy)cytidine deaminase [EC 3.5.4.5], and adenosine deaminase [EC 3.5.4.4]. Release of these enzymes was inhibited remarkably by an addition of Mg2+. Treatment in situ of E. coli cells with diazo-7-amino-l, 3-naphthalene-disulfonic acid failed to inactivate these enzymes while RNase I [EC 2.7.7.16] activity was destroyed almost completely. In contrast to conventional periplasmic proteins, enzymes of nucleoside catabolism are not released upon conversion into spheroplasts by lysozyme [EC 3.2.1.17] and EDTA. When spheroplasts were lyzed and fractionated in a medium containing Mg2+, more than half of these activities were detected in the membrane fraction. These enzymes were, however, quantitatively released into the cytoplasmic supernatant by omission of Mg2, + or by addition of Brij 58. Based on these cellular localization of these enzymes in E. coli is discussed.