INHIBITION BY DIISOPROPYLFLUOROPHOSPHATE OF A KIDNEY TRANSPORT ADENOSINE TRIPHOSPHATASE BY PHOSPHORYLATION OF A SERINE RESIDUE

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Abstract
A transport ATPase preparation from beef kidney is irreversibly inhibited by DFP. This inhibition involves phosphorylation of a serine residue. The nontransport ATPase is unaffected by DFP. The inhibition requires Mg++ and is antagonized by Ca++; these are known properties of the transport ATPase. Low concentrations of ATP protect against DFP inhibition. Pyrophosphate, CTP, GTP, ADP, and, to a slight extent, UTP also protect, but their affinities at the protecting site are at best only one tenth of that of ATP. AMP does not protect. The effects of pyrophosphate and the nucleotides suggest that a pyrophosphate group is necessary and sufficient for protection, but its affinity is influenced by the nature of the nucleoside group. K+ enhances the inhibitory effect of DFP and antagonizes the ATP protection. Strophanthidin also enhances the inhibitory effect of DFP on the transport ATPase. Na+ alone is without effect on either the DFP inhibition or the ATP protection, but it opposes the potentiating effects of K+ on the DFP inhibition. The data suggest that a reactive serine is involved at or near the substrate site of the transport ATPase; however, these studies cannot be interpreted as evidence that this serine is phosphorylated by ATP during normal catalytic activity.