Lehrstuhl Mikrobiologie, Universität Freiburg, D-79104 Freiburg, Germany.
Annu Rev Microbiol. 2011;65:631-58. doi: 10.1146/annurev-micro-090110-102801.
The fixation of inorganic carbon into organic material (autotrophy) is a prerequisite for life and sets the starting point of biological evolution. In the extant biosphere the reductive pentose phosphate (Calvin-Benson) cycle is the predominant mechanism by which many prokaryotes and all plants fix CO(2) into biomass. However, the fact that five alternative autotrophic pathways exist in prokaryotes is often neglected. This bias may lead to serious misjudgments in models of the global carbon cycle, in hypotheses on the evolution of metabolism, and in interpretations of geological records. Here, I review these alternative pathways that differ fundamentally from the Calvin-Benson cycle. Revealingly, these five alternative pathways pivot on acetyl-coenzyme A, the turntable of metabolism, demanding a gluconeogenic pathway starting from acetyl-coenzyme A and CO(2). It appears that the formation of an activated acetic acid from inorganic carbon represents the initial step toward metabolism. Consequently, biosyntheses likely started from activated acetic acid and gluconeogenesis preceded glycolysis.
将无机碳固定到有机物质中（自养）是生命的前提，也是生物进化的起点。在现存的生物圈中，还原性戊糖磷酸（卡尔文-本森）循环是许多原核生物和所有植物将 CO₂固定到生物量中的主要机制。然而，原核生物中存在五种替代的自养途径这一事实经常被忽视。这种偏见可能导致在全球碳循环模型、代谢进化假说以及地质记录解释方面的严重错误判断。在这里，我回顾了这些与卡尔文-本森循环在根本上不同的替代途径。显然，这五条替代途径的核心是乙酰辅酶 A，即新陈代谢的转盘，需要一条从乙酰辅酶 A 和 CO₂开始的糖异生途径。似乎是从无机碳形成活化的乙酸代表了向新陈代谢迈出的第一步。因此，生物合成可能是从活化的乙酸开始的，而且糖异生先于糖酵解。
