Radioassay of the folate-hydrolyzing enzyme activity, and the distribution of the enzyme in biological cells and tissues.

A sensitive radioassay method has been developed to quantitate the activity of the folate-hydrolyzing enzyme which catalyzes the hydrolysis of folic acid to pteroic acid and glutamic acid. The method is based on analyzing [2-14C]pteroic acid separated by a thin-layer chromatography on an Avicel SF cellulose plate using 0.1 M potassium phosphate buffer, pH 7.0, as a solvent. This method was found to be more sensitive than a conventional photometric method to determine the activity of the folate-hydrolyzing enzyme. High activities of the enzyme were found in Crithidia fasciculata ATCC 12857, Neurospora crassa IFO 6979 and rat liver. Smaller activities of the enzyme were widely distributed in other microbial cells and mammalian tissues.