as riboflavin and biotin into milk. Xenobiotic toxins compete for the substrate binding domain of ABCG2 potentially causing toxins to concentrate in the breast milk. In the kidney and gastrointestinal tract, it has a role in urate excretion. The protein also carries the Jr(a) antigen, which defines the Junior blood group system. Interactive pathway map Inhibition It is inhibited by some calcium channel blockers such as amlodipine, felodipine and nifedipine. The fungal toxin fumitremorgin C (FTC) inhibits the protein but has neurotoxic side effects. A synthetic tetracyclic analog of FTC called Ko-143 inhibits ABCG2. See also ATP-binding cassette transporter References Further reading External links Clusters of differentiation ATP-binding cassette transporters