Specific inhibitor and substrate specificity of alkaline phosphatase expressed in the symbiotic phase of the arbuscular mycorrhizal fungus, Glomus etunicatum

Specific inhibitor and substrate specificity of alkaline phosphatase in the arbuscule of Glomus etunicatum were investigated, and the possible role of this enzyme in the symbiosis was discussed. Mycorrhizal roots of marigold (Tagetes patula) were digested by cellulase and pectinase to separate the i ntraradical hyphae from the root tissue, and phosphatase activity was stain ed at pH 8.5 and 5.0. The activity of alkaline phosphatase (pH 8.5) in arbu scules was inhibited in the presence of beryllium, whereas that of acid pho sphatase (pH 5.0) was less sensitive to beryllium. Specificity and effectiv eness of beryllium on the alkaline phosphatase was further confirmed using fractionated (soluble and insoluble) enzyme prepared from the separated hyp hae. The soluble and insoluble alkaline phosphatases hydrolyzed phosphomono ester compounds (glucose-6-phosphate, beta-glycerophosphate, trehalose-6-ph osphate and glucose 1-phosphate) but not pyrophosphate compounds (ATP and p olyphosphate) which were hydrolyzed by acid phosphatase efficiently. The in soluble alkaline phosphatase showed high specific activity (on a protein ba sis) and high sensitivity to beryllium. Kinetic analysis of the insoluble a lkaline phosphatase suggested the involvement of this enzyme in the sugar m etabolism of the fungus due to lower Km values for sugar phosphate such as glucose-6-phosphate and trehalose-6-phosphate.