Abstract
In synthetic diets fed to weanling rats, methionine and fat must be present in a definite ratio in order to maintain a serum alkaline phosphatase activity equal to that obtained on a standard laboratory diet of animal checkers. This ratio is approximately 1:25 by weight for a diet containing 8.5% fat. Increased fat enhances, while increased methionine lowers, the serum phosphatase activity. Although in some experiments methionine was fed in concentrations sufficient to lower phosphatase activity to what has been considered definitely subnormal values, growth was good and the general condition of the animals was excellent. However, beyond certain concentrations of the amino acid, food consumption decreased and weight losses occurred. Cystine had no effect in opposing the action of methionine on serum alkaline phosphatase.