Abstract
Several recent studies of the effects of thyroxine on rat liver(1,2,3,4,5) and skeletal muscle(4) have presented evidence that the effects of thyroxine on electron transport are secondary to an effect on protein synthesis. Studies in our laboratory on rat liver(1) have shown a general thyroxine-induced increase of all components of the succinoxidase system. Since this should be a basic metabolic phenomenon, it was decided to investigate a second vertebrate class.
Methods and materials. Hubbard White Mountain chickens were placed on experiment at 4 weeks of age, treated for 4 weeks and sacrificed by severing the neck arteries. For treatment, the birds were divided into 8 groups of 5 males and 5 females, and while Groups 1–4 were kept at 70°F, Groups 5–8 were kept at 85°F. Groups 1 and 5 received the basal diet and in all other groups, iodinated casein was substituted for glucose monohydrate in the basal diet at levels of 0.05% (Groups 2 and 6), 0.10% (Groups 3 and 7) and 0.20% (Groups 4 and 8). Livers were rapidly removed following sacrifice and chilled in 20 ml of the homogenizing medium (0.25 M sucrose).
Previously described assays were used for determination of cytochrome oxidase activity(6), and reduced nicotinamide adenine dinucleotide (NADH)- and succinic-cytochrome c reductase activities (1). Succinic oxidase and NADH oxidase activities were determined polarographically. The former system contained 100 μmoles of phosphate, pH = 7.2; 40 μmoles of succinate, pH = 7.0; and 5–10 mg protein in a final volume of 2.0 ml. The latter system contained 80 μmoles of phosphate, pH = 7.4; 0.5 μmole of NADH; and 5–10 mg of protein in a final volume of 2.0 ml. The degree of “openness” to cytochrome c was determined by adding 1 μmole of cytochrome c to each system. All assays were performed on whole homogenates at 38°C.
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