Demonstration of Two Types of Proteins Synthesized in Isolated Rat‐Liver Mitochondria

Isolated rat‐liver mitochondria incorporate various labeled amino acids into two types of proteins. About one third of the incorporated radioactivity is soluble in chloroform—methanol (2:1, v/v), the other part is insoluble. The incorporation into the chloroform‐methanol‐soluble proteins is sensitive to chloramphenicol and ethidium bromide, but insensitive to cycloheximide. The rate of incorporation into the chloroform‐methanol‐soluble proteins is different from that into the insoluble proteins, depending on the time of incubation, the intactness of the mitochondria and the sucrose concentration of the incubation medium. The possibility of the existence of two different types of protein synthetic systems in mitochondria is discussed.