Abstract
Abstract Increased levels of activity for the formate activating enzyme and N5,N10-methylene FH4 dehydrogenase have been found in the leukocytes from patients with infectious mononucleosis; in addition dihydrofolic reductase, an enzyme not found in mature circulating leukocytes, has been detected in infectious mononucleosis cells. Glucose-6-phosphate dehydrogenase activity is less in infectious mononucleosis leukocytes than in normal leukocytes. These findings are similar to the results obtained in acute and chronic myelogenous leukemia and indicate that the leukocytes seen in infectious mononucleosis have the enzymatic apparatus associated with synthesis of DNA.