Protein synthesis in mitochondria. Requirements for the incorporation of radioactive amino acids into mitochondrial protein.

of inactivated (heated at 80° for 30 min.) intestinal mucosa of hens, and the optimum pH for the enzyme of mature fowl was not altered by inactivated mucosa of chicks. 3. A mixture of the enzyme preparations of chicks and mature fowl exhibited a pH-activity curve and quantitative reaction velocities which would be expected from a combination of two enzymes possessing different pH optima. 4. In rabbits the shift in pH optima for intestinal phosphatase was to lower values with increasing age, the major change taking place in the first 2 months of life. 5. There was no change in pH optima of the phosphatase of intestinal mucosa of rats as their age increased from 6 weeks to 1 year. The pH optima for the phosphatase of a preparation of the whole duodenum of 1-day-old rats were higher than those of the mucosal enzyme of older rats. 6. The pH optima for the phosphatases of bone, liver and kidney of fowl and rabbits appeared to be constant regardless of their age. The authors wish to express their indebtedness to Miss G. Ritcey for invaluable technical assistance.