[Comparison of casein utilization limited by different amino acids]

Experiments of Wistar rats were made to compare the utilization of proteins limited by sulfur-containing amino acids or isoleucine. The score of the limiting amino acid of the proteins under study was identical (0.65). The diets included 2, 5, 10, 15, 20, 25, 30, 40 and 50 g protein per 100 g diet. Depending on the protein content in the diet, the following values of net protein utilization (NPU) were obtained for protein limited by sulfur-containing amino acids: 0.680, 0.647, 0.616, 0.600, 0.562, 0.460, 0.315, 0.240, 0.210. Meanwhile, the values for protein limited by isoleucine were 0.700, 0.697, 0.600, 0.560, 0.524, 0.450, 0.340, 0.260, 0.200. Despite insignificant differences in feed consumption and weight gains in the animals, the above cited values of the NPU did not differ essentially in terms of test protein concentration under comparison. The data obtained indicate that the biological value of proteins limited by sulfur-containing amino acids does not differ from that of proteins limited by isoleucine.