Ursinus A, Steinhaus H, Höltje J V
Abteilung Biochemie, Max-Planck-Institut für Entwicklungsbiologie, Tübingen, Germany.
J Bacteriol. 1992 Jan;174(2):441-6. doi: 10.1128/jb.174.2.441-446.1992.
An LD-carboxypeptidase releasing the terminal D-Ala from UDP-MurNAc-L-Ala-D-Glu-m-A2pm-D-Ala (UDP-MurNAc-tetrapeptide) was purified from Escherichia coli to biochemical homogeneity and characterized biochemically. Final purification was achieved by nocardicin A-Sepharose affinity chromatography. An apparent molecular weight of 32,000 was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis for the enzyme, which seems to be a monomeric protein as indicated by gel filtration. The optimum pH of the enzyme was 8.4, and the pI was 5.5. The Km for UDP-MurNAc-tetrapeptide was 1.5 x 10(-4) M, and the Vmax was 0.4 nmol/min. Nocardicin A inhibited the enzyme competitively, with a Ki of 5 x 10(-5) M. Benzylpenicillin, cephalosporin C, thienamycin, and D-alanyl-D-alanine did not affect the enzyme activity. Possible functions of the enzyme for growth and division of the murein sacculus are discussed.
从大肠杆菌中纯化出一种能从UDP - MurNAc - L - Ala - D - Glu - m - A2pm - D - Ala（UDP - MurNAc - 四肽）释放末端D - Ala的LD - 羧肽酶，并对其进行了生化特性鉴定。最终通过诺卡菌素A - 琼脂糖亲和层析实现纯化。通过十二烷基硫酸钠 - 聚丙烯酰胺凝胶电泳测定该酶的表观分子量为32,000，凝胶过滤表明其似乎是一种单体蛋白。该酶的最适pH为8.4，pI为5.5。UDP - MurNAc - 四肽的Km为1.5×10⁻⁴ M，Vmax为0.4 nmol/min。诺卡菌素A竞争性抑制该酶，Ki为5×10⁻⁵ M。苄青霉素、头孢菌素C、硫霉素和D - 丙氨酰 - D - 丙氨酸不影响该酶活性。讨论了该酶在胞壁质囊生长和分裂中的可能功能。
