Kinetic mechanism and ATP‐binding site reactivity of p38γ MAP kinase

Abstract Activated p38γ MAP kinase exhibited significant basal ATPase activity in the absence of a kinase substrate, and addition of a phosphoacceptor substrate increased k cat / K m >20-fold. AMP-PCP was competitive with ATP binding and non-competitive with phosphoacceptor substrate binding. The nucleotide binding site affinity label 5′-( p -fluorosulfonylbenzoyl)adenosine (FSBA) bound stoichiometrically at Lys-56 in the ATP site of both unphosphorylated and activated p38γ. AMP-PCP only protected the activated enzyme from FSBA inactivation, implying that AMP-PCP does not bind unphosphorylated p38γ. Basal ATPase activities were also observed for activated p38α, ERK2 and JNK3 suggesting that the enzymatic mechanism may be similar for all classes of MAP kinases.