4-(FLUOROMETHYL)PHENYL PHOSPHATE ACTS AS A MECHANISM-BASED INHIBITOR OF CALCINEURIN

The compound 4-(fluoromethyl)phenyl phosphate (FMPP), recently shown t o be a mechanism-based inhibitor of prostatic acid phosphatase (Myers, J. K., and Widlanski, T. S. (1993) Science 262, 1451-1453), was exami ned for its effect on calcineurin. This compound inhibits calcineurin in a time-dependent, first order manner, Inactivation with [H-3]FMPP l ed to a specific labeling of the catalytic subunit with a stoichiometr y of 0.75 mol of label/mol of protein. A related substrate, 4-methylph enyl phosphate, is able to protect calcineurin from FMPP-mediated inhi bition. Scavenging nucleophiles, such as cysteine, do not affect the r ate of inhibition when included in the reaction, In addition, extensiv e dialysis indicates that inhibition is essentially irreversible. Thes e results demonstrate that FMPP inactivates calcineurin in a mechanism -based fashion by forming a covalent adduct with calcineurin A, the ca talytic subunit.