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A Metabolic Comparison of Cysteine and Methionine Supplements in the Diet of a Rat¹

Department of Nutrition and Food Sciences, University of Tennessee, Knoxville, TN 37996-1900

Adult male Long-Evans rats (250–300 g) were fed diets containing 15% of casein not supplemented with amino acids, supplemented with 0.505% cysteine or supplemented with 0.620% methionine for a period of 17 days. Rats fed the diets supplemented with cysteine had an increased incorporation of the ¹⁴C-radioactivity from [U-¹⁴C]alanine into liver glycogen and a decreased incorporation from [U-¹⁴C]acetate into fatty acids. Pyruvate carboxylase activity was slightly increased and citrate cleavage enzyme activity decreased in the livers of those rats fed the diets supplemented with cysteine. Rats fed diets supplemented with methionine had a decreased liver phosphoenolpyruvate carboxykinase activity. Based on these data it appears that rats fed diets supplemented with cysteine adapt metabolically to store energy as glycogen, while those fed diets supplemented with methionine tend to store energy as lipid.

KEY WORDS: • cysteine • methionine • gluconeogenesis • glycogenesis • lipogenesis • enzymes

¹ Published by permission of the Dean, College of Home Economics, and the Dean, Tennessee Agricultural Experiment Station.

Manuscript received 12 May 1982.