Purification and properties of an acid phosphomonoesterase from Neurospora crassa

Abstract

An acid phosphomonoesterase was purified 1400-fold from mycelium of Neurospora crassa with a 40% recovery. The enzyme had a pH maximum of 5.6 with [beta]-glycerol phosphate or glucosamine 6-phosphate as substrates, and cation or cofactor requirements could not be demonstrated. The substrate specificity of the enzyme was studied, using 46 compounds, [alpha]-glycerol phosphate being hydrolyzed most rapidly. When a free amino group and a phosphomonoester group were attached to adjacent carbon atoms, the compound either would not serve as a substrate or was slowly hydrolyzed. Deoxyguanosine 5'-phosphate and thymidine 5'-phosphate were not hydrolyzed although all other nucleoside monophosphates tested were able to serve as substrates. Fluoride and (+)tartrate were competitive inhibitors for the hydrolysis of [beta]-glycerol phosphate, while concentrations of thyroxine that completely inhibited the hydrolysis of acetyl phosphate did not affect the hydrolysis of [beta]-glycerol phosphate or p-nitrophenyl phosphate. No evidence was obtained for the presence of more than one phosphomonoesterase in the purified enzyme preparation. These properties distinguish this enzyme from previously described microbial phosphomonoesterases. The possibility of this acid phosphomonoesterase participating in metabolic control systems in N. crassa was discussed.