Observations on folate absorption with particular reference to folate polyglutamate and possible inhibitors to its absorption

A test system for detection of inhibitors to the enzyme which removes the glutamic acid peptide chain from folate polyglutamates (folate conjugase) is described. This utilizes the reaction between plasma conjugase and the folate polyglutamate in red blood cell haemolysate. Diphenylhydantoin and yeast extracts did not inhibit plasma conjugase. The better absorption of monoglutamate forms of folate as compared to polyglutamate forms was confirmed. Polyglutamates were absorbed normally by patients with pernicious anaemia, suggesting that conjugase enzymes (optimally active at pH 4.5) did not normally function to a significant extent in the gut lumen. Diphenylhydantoin and bicarbonate did not interfere with absorption of either mono- or polyglutamate forms of folate.