Tegumentary Phosphohydrolases of Hymenolepis diminuta

The tegumentary phosphohydrolases of Hymenolepis diminuta were examined using fructose phosphates and para-nitrophenyl phosphate as substrates. The approximate Michaelis' constants for the hydrolysis of fructose-1,6-diphosphate, fructose-1-phosphate, and para-nitrophenylphosphate are 1.36 mM, 11.78 mM, and 0.69 mM, respectively. The hydrolysis of fructose-1,6-diphosphate and fructose-1-phosphate is optimal at pH 7.0 to 7.4 while the hydrolysis of para-nitrophenylphosphate is not affected by pH over a broad range from 7.4 to 9.0. The hydrolysis of the fructose phosphates is inhibited by various phosphorylated sugars, adenosine triphosphate, adenosine monophosphate, phlorizin, molybdate, para-chloromercuribenzoate, and para-nitrophenylphosphate while the hydrolysis of para-nitrophenylphosphate is only inhibited by adenosine monophosphate and molybdate. These differences in susceptibility of the hydrolysis of these substrates to pH and to various inhibitors suggest the presence of at least 2 phosphohydrolases in the tegument. Ultrastructural localization of the enzyme activity shows both substrates to be hydrolyzed at the brush border of the tegument.