Matsuhashi M, Maruyama I N, Takagaki Y, Tamaki S, Nishimura Y, Hirota Y
Proc Natl Acad Sci U S A. 1978 Jun;75(6):2631-5. doi: 10.1073/pnas.75.6.2631.
A mutant of Escherichia coli that is deficient in D-alanine carboxypeptidase IA has been isolated. The enzyme is membrane bound and moderately sensitive to penicillin. It catalyzes in vitro both D-alanine carboxypeptidase and transpeptidase reactions. Being able to synthesize crosslinked peptidoglycan both in vivo and in vitro despite the absence of enzyme activity, the newly isolated mutant grew normally under a wide range of growth conditions. Therefore, this enzyme, like D-alanine carboxypeptidase IB, is not required for normal peptidoglycan synthesis in E. coli. The defect in the activity of D-alanine carboxypeptidase IA in the mutant however was not associated with disappearance of penicillin-binding proteins 5 and 6 (which have been shown to be D-alanine carboxypeptidase IA) or any of the other protein bands that bind [14C]penicillin G. Genetic mapping studies showed that the mutation (dacA) is located close to leuS(13.7 min) on the E. coli chromosome map. Double mutants (dacA dacB) that are deficient in both D-alanine carboxypeptidases IA and IB were obtained. These double mutants also were found to grow normally and to catalyze normal formation of crosslinked peptidoglycan.
已分离出一株缺乏D - 丙氨酸羧肽酶IA的大肠杆菌突变体。该酶与膜结合，对青霉素中度敏感。它在体外催化D - 丙氨酸羧肽酶反应和转肽酶反应。尽管缺乏酶活性，但新分离的突变体在体内和体外都能够合成交联肽聚糖，并且在广泛的生长条件下正常生长。因此，与D - 丙氨酸羧肽酶IB一样，该酶对于大肠杆菌中正常的肽聚糖合成不是必需的。然而，突变体中D - 丙氨酸羧肽酶IA的活性缺陷与青霉素结合蛋白5和6（已证明它们是D - 丙氨酸羧肽酶IA）或任何其他结合[14C]青霉素G的蛋白条带的消失无关。遗传图谱研究表明，该突变（dacA）位于大肠杆菌染色体图谱上靠近leuS（13.7分钟）的位置。获得了同时缺乏D - 丙氨酸羧肽酶IA和IB的双突变体（dacA dacB）。这些双突变体也被发现能够正常生长并催化交联肽聚糖的正常形成。
