Effect of Methionine and Other Nitrogen Sources on Biochemical Processes in the Liver

When rats were fed diets containing 12% of casein supplemented with either glycocyamine or glycine, a slight decrease was observed in their growth rate. This decrease was overcome by the addition of methionine to the respective diets. An increase was observed in the total liver protein and a corresponding decrease in liver fat when the rats were fed the casein diet supplemented with methionine. A decrease in liver protein and an increase in the percentage of liver fat was noted in rats being fed the diet supplemented with glycocyamine. The incorporation of the S35 from labeled methionine into liver was reduced when the animals were fed the casein diet supplemented with methionine and was reduced further when the casein diet was supplemented with methionine plus glycocyamine or methionine plus glycine. A working hypothesis was developed which emphasized the dual role of methionine in protein anabolism, first as an essential amino acid in the structure of tissue protein, and second as a methylating agent, possibly contributing to the energy requirements for synthesis.