Heterogeneity in the liver mitochondria of the tadpole, Rana catesbeiana.
1. The heterogeneity of liver mitochondria of the tadpoles, Rana catesbeiana, undergoing metamorphosis was investigated by a combination of pulse-chase labeling of mitochondria with [methyl-3H]thymidine and centrifugation of mitochondria on a density gradient of metrizamide. 2. The liver mitochondria of tadpole at premetamorphic stage are separated into two populations with mean densities of 1.128 (M2) and 1.112 (M3). 3. At metamorphic stage a population with mean densities of 1.174 (M1) appears additionally. 4. The activity of mitochondria to take up [methyl-3H]thymidine in vivo is 2-3 times higher at metamorphic stage than at premetamorphic stage. 5. The M1 population has a prominently high activity to take up L-[4.5-3H]leucine in vitro and also a high specific activity of cytochrome c oxidase. 6. These findings suggest that the mitochondrial populations found are of alternate stages in the mitochondrial maturation.