Incorporation of 65Zn in the sub-cellular fractions of the liver and spontaneously occurring mammary tumours of mice after the injection of zinc–glycine containing 65Zn

Abstract

The distribution of Zn65 in the nuclear, mitochondrial and supernatant (soluble proteins plus microsomes) fractions of mammary tumors and livers of mice, 1 and 3 days after the mice have been injected with the isotope in the form of a Zn65-containing zinc-glycine complex, was studied. The results are expressed as Zn65/mg. of nitrogen in any particular fraction, and also as a special ratio: (Zn65/nitrogen in the sub-cellular fraction) Zn65/nitrogen in the whole mash). Zn65 was found in nuclear, mitoehondrial and supernatant fractions of mammary tumors and livers. The tumor cells showed a remarkably uniform distribution of Zn65 between the 3 fractions, but the liver supernatant fractions contained 3 or 4 times as much Zn65 as did the nuclei and mitochondria. Part of the Zn65 incorporated into these tissues can be removed by dialysis in slightly acid or alkaline solutions but not normally at pH 7.4. The results of these dialyses are consistent with the view that the zinc is mainly bound to the imidazole groups of proteins. About four-fifthsof the Zn65 present in both the liver and the tumor is freely exchangeable with Zn2+ ions at pH 7.4 and can be removed by dialysing the mash against buffers containing excess of exchangeable zinc or the zinc-binding ethylenediaminetetra-acetic acid. About one-sixth of the Zn65 in these tissues could not be removed by exchange or by combination with ethylenediaminetetra-acetic acid, and this fraction probably represents Zn65 in zinc bound to protein.