It was initially assumed that the tetracycline nucleus originated by the polyketide pathway from acetylor malonyl-CoA. Evaluation of the results of experiments with labelled precursors and on the regulation of presumed key enzyme systems, however, has led to the conclusion that the situation is more complex than was first thought. It is suggested that chlortetracycline does not fit into the category of the so-called secondary metabolites and should be regarded rather as an 'excessive metabolite' produced by variation in the control of certain key primary pathways. The experimental evidence on control of pathways during the various phases of the bacterial growth cycle is reviewed.

中文翻译：

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四环素的生物合成

最初假设四环素核起源于来自乙酰或丙二酰辅酶 A 的聚酮化合物途径。然而，对标记前体的实验结果和推测的关键酶系统的调节结果的评估得出的结论是，情况比最初想象的要复杂。有人认为金霉素不属于所谓的次生代谢物的范畴，而应被视为由某些关键主要途径的控制发生变化而产生的“过量代谢物”。回顾了在细菌生长周期的各个阶段控制通路的实验证据。