Polypeptide turnover in brown adipose tissue mitochondria during acclimation of rats to cold

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Abstract
During the initial phase of cold-induced growth of brown adipose tissue in rats, there is a selective increase in the incorporation of infused [3H]phenylalanine into mitochondrial membrane polypeptides of MW 25,000-35,000. This is interpreted as a selective increase in the synthesis of a 32,000 polypeptide, of which the proportion increases in brown adipose tissue mitochondria when the tissue has a high capacity for thermogenesis, as in the cold-acclimated rat. This polypeptide is associated with the thermogenic proton conductance pathway. A simultaneous selective decrease in degradation or the formation from larger mitochondrial membrane polypeptides may also occur. In fully cold-acclimated rats, in which a new steady state is reached, there is a general increase in turnover of all mitochondrial membrane polypeptides but no marked selective changes in pattern of incorporation of radioactive amino acid or in rates of disappearance of radioactivity from groups of polypeptides. Isolated brown adipose tissue mitochondria incorporate [3H]phenylalanine principally into polypeptides of MW 25,000-35,000. No change in the pattern of incorporation occurred in mitochondria isolated from brown adipose tissue of cold-exposed (2 wk) rats. The cold-induced change in mitochondrial composition in brown adipose tissue, which occurs at the same time as tissue and mitochondria growth, is probably brought about by selective changes in cytosolic protein synthesis and possibly also by selectively altered degradation or conversion of mitochondrial polypeptides.

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