Vimr E R, Miller C G
J Bacteriol. 1983 Mar;153(3):1252-8. doi: 10.1128/jb.153.3.1252-1258.1983.
Mutants of Salmonella typhimurium deficient in dipeptidyl carboxypeptidase have been isolated by screening for clones unable to use N-acetyl-L-alanyl-L-alanyl-L-alanine (AcAla3) as the sole nitrogen source. An insertion of the transposable element Tn10 near dcp (the locus coding for dipeptidyl carboxypeptidase) has been isolated and used to map the locus in the interval between purB and trp, an otherwise genetically silent region of the S. typhimurium map. All dcp mutants could still grow using N-acetyl-L-alanyl-L-alanyl-L-alanyl-L-alanine (AcAla4) as the sole nitrogen source. Crude extracts from the dcp mutants failed to hydrolyze AcAla3 but retained approximately 80% of the wild-type activity toward AcAla4. Several lines of evidence indicate that hydrolysis of AcAla4 in the dcp mutant results from the action of a new peptidase distinct from dipeptidyl carboxypeptidase. A mutant strain lacking dipeptidyl carboxypeptidase in addition to peptidases N, A, B, and D showed reduced protein breakdown during carbon starvation compared with a strain lacking only peptidases N, A, B, and D.
通过筛选无法利用N-乙酰-L-丙氨酰-L-丙氨酰-L-丙氨酸（AcAla3）作为唯一氮源的克隆，分离出了鼠伤寒沙门氏菌中二肽基羧肽酶缺陷的突变体。已分离出转座子Tn10在dcp（编码二肽基羧肽酶的基因座）附近的插入，并用于将该基因座定位在purB和trp之间的区间，这是鼠伤寒沙门氏菌图谱中一个原本基因沉默的区域。所有dcp突变体仍能利用N-乙酰-L-丙氨酰-L-丙氨酰-L-丙氨酰-L-丙氨酸（AcAla4）作为唯一氮源生长。dcp突变体的粗提取物无法水解AcAla3，但对AcAla4的活性仍保留约80%的野生型活性。几条证据表明，dcp突变体中AcAla4的水解是由一种不同于二肽基羧肽酶的新肽酶的作用导致的。与仅缺乏肽酶N、A、B和D的菌株相比，除了肽酶N、A、B和D外还缺乏二肽基羧肽酶的突变菌株在碳饥饿期间蛋白质分解减少。
