作者:John F. DAVEY、Peter W. TRUDGILL
DOI:10.1111/j.1432-1033.1977.tb11373.x
日期:1977.3
Acinetobacter TD63 was one of some thirty organisms isolated by elective culture with trans‐cyclohexan‐1,2‐diol as sole source of carbon. The great majority of these isolates displayed the same growth spectrum as Nocardia globerula CL1 and Acinetobacter NCIB 9871 being capable of utilizing trans‐cyclohexan‐1,2‐diol, 2‐hydroxycyclohexan‐1‐one, cyclohexanol, cyclohexanone, 1‐oxa‐2‐oxocycloheptane and adipate and were assumed to use well described metabolic pathways.
Acinetobacter TD63 was distinctive in being incapable of growth with cyclohexanol, cyclohexanone or 1‐oxa‐2‐oxocycloheptane and because of this it was hoped that it would display an alternative pathway for the oxidation of trans‐cyclohexan‐1,2‐diol.
Studies with cell extracts have shown the presence of inducible dehydrogenase for the conversion of trans‐cyclohexan‐1,2‐diol to 2‐hydroxycyclohexan‐1‐one and cyclohexan‐1,2‐dione and of 6‐oxohexanoate to adipate. These enzymes are linked into a metabolic sequence by the action of a monooxygenase of broad specificity but efficiently capable of converting 2‐hydroxycyclohexan‐1‐one into the lactone 1‐oxa‐2‐oxo‐7‐hydroxycycloheptane that spontaneously rearranges to yield 6‐oxohexanoate.
An enzyme capable of attacking cyclohexan‐1,2‐dione (mono‐enol) in the absence of an electron donor or oxygen has also been detected. Evidence has been presented indicating that this enzyme catalyses a keto‐enol tautomerization between cyclohexan‐1,2‐dione (mono‐enol) and cyclo‐hexan‐1,2‐dione (mono‐hydrate) and is not involved in the pathway of ring cleavage.
The failure of Acinetobacter TD63 to grow with cyclohexanol, cyclohexanone or 1‐oxa‐2‐oxocycloheptane is due not to this organism possessing a distinctive metabolic sequence but to a narrow inducer specificity coupled with an inability to form a lactone hydrolase enabling it to cleave the stable 1‐oxa‐2‐oxocycloheptane which is an intermediate in the established pathway of cyclohexanol and cyclohexanone oxidation.
Acinetobacter TD63是通过选择性培养从数十种分离的菌株中获得的,trans‐环己烷1,2-二醇是其唯一碳源。绝大多数分离株与Nocardia globerula CL1和Acinetobacter NCIB 9871具有相同的生长谱,能够利用trans‐环己烷1,2-二醇、2-羟基环己烷1-酮、环己醇、环己酮、1-氧-2-氧环庚烷和己二酸,并且假定其使用了描述清楚的代谢途径。
Acinetobacter TD63的独特之处在于其不能以环己醇、环己酮或1-氧-2-氧环庚烷为底物生长。因此,人们希望它能展示一种替代途径,用于trans‐环己烷1,2-二醇的氧化。
细胞提取物的研究表明,存在一种可诱导的脱氢酶,能够将trans‐环己烷1,2-二醇转化为2-羟基环己烷1-酮和环己烷1,2-二酮,并将6-氧己酸转化为己二酸。这些酶通过一种广谱单加氧酶的作用连接到一个代谢序列中,这种酶能够高效地将2-羟基环己烷1-酮转化为内酯1-氧-2-氧-7-羟基环庚烷,该化合物自发重排生成6-氧己酸。
还检测到一种能够攻击环己烷1,2-二酮(单烯醇)的酶,这种攻击不需要电子供体或氧气。证据表明,该酶催化环己烷1,2-二酮(单烯醇)与其单水合物之间的酮-烯醇互变异构,而不参与环裂解途径。
Acinetobacter TD63不能以环己醇、环己酮或1-氧-2-氧环庚烷为底物生长,原因不在于该菌株具有独特的代谢序列,而在于其诱导剂特异性狭窄,并且无法形成能够裂解稳定中间体1-氧-2-氧环庚烷(环己醇和环己酮氧化途径中建立的中间体)的酯酶。