A possible minor route of ornithine catabolism in Aspergillus nidulans might begin with the ornithine decarboxylase reaction and end with the succinic semialdehyde dehydrogenase reaction. It is therefore of interest that the putative structural genes for these two enzymes, puA and ssuA, respectively, are tightly linked group II. However, this linkage is unlikely to have regulatory significance because ileA, the structural gene for threonine dehydratase, separates them. The gene order in this region is ssuA-ileA-puA-mauB-anB. (mauB- mutations result in loss of monoamine oxidase whilst anB- mutations lead to aneurin auxotrophy.) 2. An auxotrophy for ornithine or putrescine in A. nidulans occurs in double mutants lacking arginase and blocked before ornithine in the arginine biosynthetic pathway. Some residual ornithine synthesis in such double mutants can be catalysed by ornithine delta-transaminase, especially if it is synthesised constitutively.

译文

构巢曲霉鸟氨酸分解代谢的一种可能的次要途径可能始于鸟氨酸脱羧酶反应,并以琥珀酸半醛脱氢酶反应结束。因此,令人感兴趣的是,这两种酶的推定结构基因分别是puA和ssuA,是紧密相连的II组。然而,这种连接不太可能具有调节意义,因为苏氨酸脱水酶的结构基因ileA将它们分离。该区域的基因顺序为ssuA-ileA-puA-mauB-anB。(mauB突变会导致单胺氧化酶的丢失,而anB突变会导致神经营养缺陷。) 2。A.Niddulans中鸟氨酸或腐胺的营养缺陷型发生在缺乏精氨酸酶的双突变体中,并且在精氨酸生物合成途径中鸟氨酸之前被阻断。此类双突变体中的某些残留鸟氨酸合成可以由鸟氨酸 δ-转氨酶催化,特别是如果它是组成型合成的。

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