[86] Formiminotransferase-cyclodeaminase: A bifunctional enzyme from porcine liver

This chapter discusses the formiminotransferase-cyclodeaminase enzyme. Formiminotransferase-cyclodeaminase is a bifunctional enzyme from porcine liver. This enzyme was first isolated from acetone powders of pig liver and later obtained in crystalline form from frozen or fresh liver. Both formiminotransferase and cyclodeaminase are assayed by spectrophotometric measurement of 5,10-methenyltetrahydrofolate; the final product of the sequential reactions. The transferase activity is measured by chemical conversion of the product formiminoH4folate to methenylH4folate, while the cyclodeaminase assay involves monitoring the conversion of added 5-formiminoH4folate to 5,10-methenylH4folate with a recording spectrophotometer. Preparations of (±)-tetrahydrofolate can be obtained and purified by several methods and stored in 0.5 M 2-mercaptoethanol-containing buffer, such as phosphate or triethanolamine-HC1. Formiminoglutamate is prepared by dissolving the hemibarium salt in water, adding 10% molar excess of solid Na2SO4, and removing the barium sulfate by centrifugation. The relatively unstable formiminotetrahydrofolate is prepared enzymically. The purification method described in this chapter does not require the preparation of acetone powders, but incorporates a modified pH precipitation in sodium acetate as used by Tabor and Wyngarden.