Effect of vitamin B-12 deprivation on the rates of synthesis and degradation of rat liver fatty acid synthetase

Eugene P. Frenkel, Richard L. Kitchens, John M. Johnston, Rene Frenkel

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To characterize the basis for the increased hepatic fatty acid synthetase activity in vitamin B-12 deprivation, the content and rates of synthesis and degradation for the enzyme were determined. Animals were in a dietary steady state on normal chow or a B-12-deprived diet; animals on the latter diet were further divided into a "supplemented" group given B-12 and those "B-12-deprived." The B-12-deprived animals had tissue B-12 depletion. Both total and specific activity of fatty acid synthetase were increased in the B-12-deprived animals, and this was due to increased enzyme protein. Rates of synthesis and degradation were studied in each group after a pulse of 20 μCi of l-[U-14C]leucine. Radioactivity was determined in the immunoprecipitate of the purified enzyme. Relative rates of synthesis in the B-12-deprived group were increased 8.8-fold over the normal and 3.6-fold over the B-12-supplemented group. Degradation of hepatic fatty acid synthetase was 63 hr (t 1 2) in the normal and 65 hr in the B-12-supplemented group. The t 1 2 in the B-12-deprived group was 35 hr. Degradation rates for the soluble protein pool were not affected by B-12 deprivation. The rate constant for synthesis of hepatic fatty acid synthetase in the B-12-deprived group was 14-fold that of the normal and 6-fold that of the B-12-supplemented animals. Thus, although vitamin B-12 deprivation results in increased rate of degradation of fatty acid synthetase, enzyme synthesis is markedly increased yielding a severalfold net increase in synthetase content and activity.

Original languageEnglish (US)
Pages (from-to)607-613
Number of pages7
JournalArchives of Biochemistry and Biophysics
Issue number2
Publication statusPublished - 1974


ASJC Scopus subject areas

  • Biochemistry
  • Biophysics
  • Molecular Biology

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