Some plants and marine organisms syntehsize fatty acids with an odd number of carbon atoms. The final round of b oxidation of these fatty acids forms propionyl-CoA, wich is converted to succinyl-CoA for entry the citric acid cycle. Propionate or propionyl-CoA is also produced by oxidation of the amino acids isoleucine, valine and methionine.

Succinyl-CoA cannot undergo net degradation by the citric acid cycle, it must first be converted either to pyruvate or directly to acetyl-CoA. But since it's a citric acid intermediate, it can contribute to the number of active citric acid cycles.