Enzymatic characteristics of an ApaH-like phosphatase, PrpA, and a diadenosine tetraphosphate hydrolase, ApaH, from Myxococcus xanthus

We characterized the activities of the Myxococcus xanthus ApaH-like phosphatases PrpA and ApaH, which share homologies with both phosphoprotein phosphatases and diadenosine tetraphosphate (Ap₄A) hydrolases. PrpA exhibited a phosphatase activity towards p-nitrophenyl phosphate (pNPP), tyrosine phosphopeptide and tyrosine-phosphorylated protein, and a weak hydrolase activity towards Ap_nA and ATP. In the presence of Mn²⁺, PrpA hydrolyzed Ap₄A into AMP and ATP, whereas in the presence of Co²⁺ PrpA hydrolyzed Ap₄A into two molecules of ADP. ApaH exhibited high phosphatase activity towards pNPP, and hydrolase activity towards Ap_nA and ATP. Mn²⁺ was required for ApaH-mediated pNPP dephosphorylation and ATP hydrolysis, whereas Co²⁺ was required for Ap_nA hydrolysis. Thus, PrpA and ApaH may function mainly as a tyrosine protein phosphatase and an Ap_nA hydrolase, respectively.