The hepatic activities of 1-carbon enzymes during the chronic administration of diethylnitrosamine, 2-acetylaminofluorene, and n,n-dimethyl-4-aminoazobenzene to rats.

The levels of seven enzymes involved in the metabolism of 1-carbon compounds and their precursors were investigated in the cytoplasmic fractions of the livers of rats receiving the hepatocarcinogens diethylnitrosamine, 2-acetylaminofluorene, and 7V,./V-dimethyl-4-aminoazobenzene for 1 to 5 weeks. The enzymes studied included serine hydroxymethylase, dihydrofolate reducÃ-ase (H2-folate reducÃ-ase), formylase, methylene-H4-folale dehydrogenase, formiminoglutamic acid transferase, urocanase, and hislidase. The levels of formiminoglulamic acid Iransferase and urocanase were found lo be significanlly lower in Ihe livers of rals Irealed with each of the hepatocarcinogens for 3 to 5 weeks lhan in Ihe livers of corresponding conlrol rats. The hepatic activilies of formylase, methylene-H4-f oÃ-ale dehydrogenase, and hislidase were decreased during Ihe chronic administration of diethylnilrosamine and 2-acetylaminofluorene bui noi by Ihe chronic feeding of ./VVV-dimelhyl-4-aminoazobenzene; however, Ihe low-prolein, low-riboflavin diel used as a control diet in the aminoazo dye experiments also led to low hepalic levels of Ihese 3 enzymes. Administralion of diethylnitrosamine and ./V,./V-dimelhyl-4-aminoazobenzene lo rals for 3 weeks led lo a slighl but significant increase in Ihe hepalic levels of H2 -folale reducÃ-ase, in comparison lo the corresponding levels in livers of conlrol rals; the feeding of 2-acelylaminofluorene appeared to have no significant effect on hepatic HZ-folate reducÃ-ase activily. None of Ihe carcinogens invesligaled appeared lo have a significanl effecl on the hepatic levels of serine hydroxymethylase. The administration of a choline-deficient diel lo weanling rals for 5 weeks produced significant decreases in Ihe hepatic levels of formylase, methylene-H4folate dehydrogenase, hislidase, urocanase, and formimino glulamic acid Iransferase; Ihe choline deficiency produced no effect on the hepatic levels of serine hydroxymelhylase and H2-folate reducÃ-ase. The results indicale lhal chronic administration to rats of eilher a hepatocarcinogenic or methyl-deficienl regimen decreased Ihe hepalic levels of five