Folic acid metabolism in vitamin B12-deficient sheep. Effects of injected methionine on liver constituents associated with folate metabolism.
1. The effects of injected l-methionine (2g every second day for 28 days) on liver folates and other constituents of liver associated with folate metabolism were studied in vitamin B(12)-deficient ewes and their pair-fed controls receiving vitamin B(12). The dose rate of methionine used was sufficient to restore almost to normal the elevated excretion in the urine of formiminoglutamate in the deficient animals. 2. Liver folates active for Lactobacillus casei, Streptococcus faecalis R and Pediococcus cerevisiae were severely depressed in deficient livers and were partly restored by methionine. Analysis of the folates after ion-exchange chromatography showed that the major effect of methionine was to increase the concentrations of tetrahydrofolates and formyltetrahydrofolates. Methyltetrahydrofolates were also increased, but there was no effect of methionine on the small amounts of incompletely reduced folates present in deficient livers. The folates present were predominantly penta-, hexa- and hepta-glutamates whether or not animals received vitamin B(12) or methionine. 3. Concentrations of ATP, NAD(+), NADH and NADPH were lower in freeze-clamped liver from vitamin B(12)-deficient sheep than in liver from pair-fed, vitamin B(12)-treated sheep. These changes were not affected by methionine which was also without effect on the elevated K(+)/Na(+) ratios found in deficient livers. 4. The livers of vitamin B(12)-deficient animals contained lower concentrations of choline and higher concentrations of lipid than their pair-fed controls. These effects were reversed by methionine.