Cyclohexanedione modification of arginine at the active site of Aspergillus ficuum phytase

Reaction of Aspergillus ficuum phytase with the arginine specific modifier 1,2-cyclohexanedione causes a rapid loss of activity. The inactivation can be partially reversed by 0.2 M hydroxylamine and exhibits pseudo-first order kinetics. The reaction order and second order rate constant of inactivation were 0.87 and 6.72 M-1 Min-1, respectively. Amino acid analysis of modified phytase indicates that about 7 arginine of the total 19 were modified. While the chymotryptic maps of treated and untreated phytase were virtually identical, the tryptic maps had 4 peaks of altered mobility. An Arg containing tripeptide was identified in the phytase which is also present in other phosphohydrolases and may represent one of the labile Arg involved in the formation of the active site