Distribution of copper and zinc among protein fractions in the cytoplasm of rat tissues.

Supernatant preparations from the liver, small intestine, and skeletal muscle of normal rats were separated on Sephadex G-150 into six Cu and Zn containing protein fractions with molecular weights of about 250,000, 153,000, 73,000, 41,000, 22,000, and 10,000. Small differences in molecular weight and metal binding were observed between tissues, but the corresponding fractions from all three tissues were generally very similar. Age affected the distribution of both metals, particularly in liver; growth from the weanling to adult stage was accompanied by the transfer of considerable amounts of Cu and Zn from the 10,000 to the 22,000 fraction. A small influence of sex on the distribution was found in skeletal muscle. After injection of 65Zn radioactivity initially entered the 10,000 fraction in liver; it was then transferred to the region of the 73,000 fraction and entered the 22,000 fraction most slowly. The metabolic importance and probable nature of the various fractions is discussed.