4-(Fluoromethyl)phenyl Phosphate Acts as a Mechanism-based Inhibitor of Calcineurin

Abstract

The compound 4-(fluoromethyl)phenyl phosphate (FMPP), recently shown to be a mechanism-based inhibitor of prostatic acid phosphatase (Myers, J.K., and Widlanski, T.S. (1993) Science 262, 1451-1453), was examined for its effect on calcineurin. This compound inhibits calcineurin in a time-dependent, first order manner. Inactivation with [3H]FMPP led to a specific labeling of the catalytic subunit with a stoichiometry of 0.75 mol of label/mol of protein. A related substrate, 4-methylphenyl phosphate, is able to protect calcineurin from FMPP-mediated inhibition. Scavenging nucleophiles, such as cysteine, do not affect the rate of inhibition when included in the reaction. In addition, extensive dialysis indicates that inhibition is essentially irreversible. These results demonstrate that FMPP inactivates calcineurin in a mechanism-based fashion by forming a covalent adduct with calcineurin A, the catalytic subunit.