Further Investigations on the p-Nitrophenylphosphatase Activity of Intact Ehrlich Ascites Tumor Cells

Abstract

The substrate specificity and the effects of nucleotides and SH-blocking agents on the p-nitro- phenylphosphatase activity of intact Ehrlich ascites tumor cells (EAT) cells were studied, ᴅʟ-β- Glycerophosphate, o-phosphoethanolamine, cholinephosphate, glucose-6-phosphate, o-carboxyphenyl- phosphate,, phosphoenolpyruvate and AMP were not attacked by intact cells. ATP > GTP > UTP > PPi > pNPP were cleaved with decreasing velocity. A stimulation of the cleavage of p-NPP by the following nucleotides was observed with decreasing effectivity: ATP > ADP > GTP > UTP; AMP was ineffective. The phosphatase activity was not affected by malate, tartrate and glutathion disulfide. The SH blocking agents diamide and thimerosal were more effective in­hibitors of the pNPPase than of the ATPase activity, whereas the hydrolysis of ATP is more affected by the ATP analog adenylylimidodiphosphate. The present data are best compatible with a double headed enzyme: Both active sites interact with ATP, only one is active against p-NPP and sensitive against SH-blocking agents.