Organic anions are chemically heterogeneous substances possessing a carbon backbone and a net negative charge.  Organic anions are conjugate bases of organic acids. The following table lists some of the organic anions and their conjugate acids which are substrates of the organic acid transporter (OAT) family of transmembrane proteins.
||Conjugate Organic Acids
(acidic proton is shown in red)
- Sekine T, Cha SH, Endou H (July 2000). "The multispecific organic anion transporter (OAT) family". Pflugers Arch. 440 (3): 337–50. PMID 10954321.