The percentages of 12 amino acids in rat fibrosarcoma and its normal homologous tissue have been determined by microbiological methods. The most significant differences found were a markedly higher content of arginine and glycine, an increase in threonine, and a lower content of histidine and methionine in the malignant than in the normal tissue. Since the amino acids were calculated for the tissues corrected for moisture, ash, fat, collagen and elastin, they were assumed to be approximately the values for the cellular proteins. No significant differences in the amino acid composition were observed for fibrosarcomas grown in four different sites in male and female (Long-Evans) rats obtained originally from the same source but maintained for many years on different diets in separate colonies. The possible physiological significance of these experimental results has been discussed.

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Paper 58. For Paper 57, see Dunn et al (1). This work was aided by grants from the American Cancer Society through the Committee on Growth, National Research Council, and from the Cancer Institute, University of California. The authors are indebted to Dr. M. N. Camien for helpful suggestions.

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