PHOTOAFFINITY-LABELING OF PROTEIN PHOSPHATASE-2A, THE RECEPTOR FOR A TUMOR PROMOTER OKADAIC ACID, BY [27-H-3]METHYL 7-O-(4-AZIDOBENZOYL)OKADAATE

The interaction of okadaic acid and a protein phosphatase, which is the receptor for a tumor promoter, okadaic acid, was studied. [27-3H]-Methyl 7-O-(4-azidobenzoyl)okadaate was synthesized and protein phosphatase 2A, which consists of two regulatory subunits of 65 kDa and 42 kDa and a catalytic subunit of 37 kDa, was purified from bovine brain. After UV irradiation of the reaction mixture, [3H]methyl 7-O-(4-azidobenzoyl)-okadaate covalently bound to the catalytic subunit, but not to the two regulatory subunits. These results strongly suggest that okadaic acid, a potent inhibitor of protein phosphatases, binds specifically to the catalytic subunit rather than to the other regulatory subunits. © 1990.