3-Hydroxypropionate cycle

A fourth pathway has been discovered for CO₂ assimilation in bacteria, the 3-hydroxypropionate cycle. In this cycle, CO₂ is fixed by acetyl-CoA and propionyl-CoA carboxylases eventually forming Malyl-CoA. This is split into acetyl-CoA, to replenish the cycle, and glyoxylate, for use in cell carbon. The electron donors and the nature of the enzymes that catalyze many of the steps are at this time unclear. Past research had demonstrated this pathway only in Chloroflexus, a nonsulfur photosynthetic bacterium, but recent work [1] has detected the pathway in several autotrophic archaea. It seems the pathway is more widespread than previously thought.

Figure 1 - The 3-hydroxypropionate cycle. The areas in blue denote the steps where carbon dioxide is incorporated.

[1]http://jb.asm.org/cgi/content/abstract/181/4/1088

这篇文献见这里：

Presence of Acetyl Coenzyme A (CoA) Carboxylase and Propionyl-CoA Carboxylase in Autotrophic Crenarchaeota and Indication for Operation of a 3-Hydroxypropionate Cycle in Autotrophic Carbon Fixation