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Folic acid metabolism in vitamin B12-deficient sheep. Effects of injected methionine on liver constituents associated with folate metabolism.

ABSTRACT: 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.

SUBMITTER: Smith RM

PROVIDER: S-EPMC1168216 | biostudies-other | 1974 Jul

REPOSITORIES: biostudies-other

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Project description:1. Metabolism of folate was studied in six ewes in an advanced state of vitamin B(12) deficiency as judged by voluntary food intake and in their pair-fed controls receiving vitamin B(12). A group of four animals that were maintained throughout the experiment at pasture was also studied. 2. After 34-40 weeks on the cobalt-deficient diet urinary excretion of formiminoglutamate by four deficient animals was about 3.2mmol/day and this was not significantly decreased by injection of three of them with about 4.5mug of [2-(14)C]folate/kg body weight per day for 5 days. Three days after the last injection retention of [2-(14)C]folate by the livers of the deficient animals (5.5% of the dose) was lower than that of their pair-fed controls (26% of the dose) but there was no evidence of net retention of injected folate in the livers of either group. Urinary excretion of (14)C indicated that renal clearance of folate may have been impaired in very severe vitamin B(12) deficiency. 3. As estimated by microbiological assays total folates in the livers of animals at pasture (12.9mug/g) included about 24% of 5-methyltetrahydrofolate as compared with about 72% of a total of 12.5mug/g in three further ewes fed on a stock diet of wheaten hay-chaff and lucerne-chaff. Liver folates of vitamin B(12)-deficient animals (0.5mug/g) included about 88% of 5-methyltetrahydrofolate as compared with about 51% of a total of 5.2mug/g in pair-fed animals treated with vitamin B(12). 4. Chromatography of liver folates of the pair-fed animals permitted quantitative estimates of the pteroylglutamates present. The results showed that the vitamin B(12)-deficient livers were more severely depleted of tetrahydrofolates and formyltetrahydrofolates than of methyltetrahydrofolates and that as the deficiency developed they were more severely depleted of the higher polyglutamates than of the monoglutamate within each of these classes. Results from animals injected with [2-(14)C]folate indicated an impairment of the exchange between pteroylmonoglutamates and pteroylpolyglutamates in the livers of deficient animals. 5. In vitamin B(12)-deficient animals with food intakes below 200g/day some of the liver folates were not completely reduced and some degradation of pteroylpolyglutamates was detected. The latter condition may have been associated with fatty liver. 6. The results are discussed in relation to current theories of vitamin B(12)-folate interactions.

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Folic acid metabolism in vitamin B12-deficient sheep. Effects of injected methionine on liver constituents associated with folate metabolism.

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