3-Hydroxypropionate bicycle

Many photosynthetic life forms (plants, algae, phototrophic and chemoautotrophic bacteria, and archaea) require a way to utilize carbon into their metabolic pathways.

In the 3-hydroxypropionate bicycle, photosynthetic organisms like Chloroflexus aurantiacus, fix CO2 and bicarbonate (HCO3− ) as part of their metabolic processes.

The overall reaction of the 3-hydroxypropionate pathway is 3 HCO−3 + 5 ATP + 6 NADPH + 1 quinone → 1 pyruvate + 6 NADP + 1 quinoneH2 + 3 ADP + 3 phosphate + 2 AMP + 2 pyrophosphate.

Glyoxylate is incorporated into beta-methylmalyl-coA which is then split, again through a series of reactions, to release pyruvate as well as acetate, which is used to replenish the cycle.

[3] This pathway has been demonstrated in Chloroflexus, a nonsulfur photosynthetic bacterium; however, other studies suggest that 3-hydroxypropionate bicycle is used by several chemotrophic archaea.