Abstract
Mn (III) -acid phosphatase [EC 3.1.3.2] from sweet potato was inactivated by diethylpyrocarbonate (DEPC) in the presence of the F- ion.Upon treatment of the inactivated enzyme with NH2OH, the enzyme activity was significantly restored. The difference absorption spectra of the modified vs. native enzyme preparations, both in the presence and absence of the F- ion, exhibited two prominent peaks at around 242 and 275 nm.The pH-dependence of the inactivation rate suggested that an amino acid residue having a pK value of approximately 7.3 was involved in the inactivation. These results indicate that the inactivation was due to the modification of histidine residues. The correlation between the spectral change at 242 nm and the activity change of theenzyme in the presence and absence of the F- ion revealed that 1 histidine residue per subunit was essential for the enzyme activity. The inactivation by DEPC occurred only in the presence of the F- ion, which has been found to interact with the Mn in the active site, suggesting that the histidine residue to be modified is located at the activesite of the enzyme.
