Irreversible inhibition of water transport in erythrocytes by fluoresceinmercuric acetate

Fluoresceinmercuric acetate (FMA) is approximately 5 times more potent than p-chloromercuribenzene sulfonate (PCMBS) in inhibiting water transport across human erythrocyte membranes. Half maximal inhibition occurred at approximately 60 m. While cysteine fully reversed the inhibition induced by p-chloromercuribenzene sulfonate it had no effect on the inhibition induced by fluoresceinmercuric acetate. A comparison of the structures of fluoresceinmercuric acetate and p-chloromercuribenzene sulfonate suggests that either there are two sulfhydryl groups in close proximity or the larger aromatic ring structure of fluoresceinmercuric acetate causes tighter binding to one sulfhydryl group at the active site.