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Zinc-, copper- and cadmium-binding protein in Ehrlich ascites tumour cells.

ABSTRACT: The properties of Ehrlich ascites tumour cells exposed in vivo to cadmium were investigated as a function of the zinc status of the host animals. Tumour-cell growth was inhibited by cadmium in both zinc-sufficient and zinc-deficient animals. However, cells in zinc-sufficient tumours accumulate much less cadmium than those in deficient tumours. The subcellular distributions of cadmium and zinc do not depend on zinc status. Cadmium and zinc are bound to a low-molecular-weight protein with properties similar to metallothionein. Without exposure to cadmium, a zinc- and copper-binding protein is still present that behaves like a metallothionein. This protein can rapidly bind cadmium added to Ehrlich cells in vitro. It is shown that the zinc- and copper-binding protein contains free thiol groups. Ehrlich cells isolated from cadmium-treated animals are viable and show normal incorporation of uridine into RNA, but the cellular uptake of thymidine and its incorporation into DNA are inhibited.

SUBMITTER: Koch J

PROVIDER: S-EPMC1161921 | biostudies-other | 1980 Jul

REPOSITORIES: biostudies-other

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Host zinc metabolism and the Ehrlich ascites tumour. Zinc redistribution during tumour-related stress.

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Regulation of glutathione metabolism in Ehrlich ascites tumour cells.

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INHIBITION OF PRUINE PHOSPHORIBOSYLTRANSFERASES OF EHRLICH ASCITES-TUMOUR CELLS BY 6-MERCAPTOPURINE.

Project description:1. The formation of adenosine 5'-phosphate, guanosine 5'-phosphate and inosine 5'-phosphate from [8-(14)C]adenine, [8-(14)C]guanine and [8-(14)C]hypoxanthine respectively in the presence of 5-phosphoribosyl pyrophosphate and an extract from Ehrlich ascites-tumour cells was assayed by a method involving liquid-scintillation counting of the radioactive nucleotides on diethylaminoethylcellulose paper. The results obtained with guanine were confirmed by a spectrophotometric assay which was also used to assay the conversion of 6-mercaptopurine and 5-phosphoribosyl pyrophosphate into 6-thioinosine 5'-phosphate in the presence of 6-mercaptopurine phosphoribosyltransferase from these cells. 2. At pH 7.8 and 25 degrees the Michaelis constants for adenine, guanine and hypoxanthine were 0.9 mum, 2.9 mum and 11.0 mum in the assay with radioactive purines; the Michaelis constant for guanine in the spectrophotometric assay was 2.6 mum. At pH 7.9 the Michaelis constant for 6-mercaptopurine was 10.9 mum. 3. 25 mum-6-Mercaptopurine did not inhibit adenine phosphoribosyltransferase. 6-Mercaptopurine is a competitive inhibitor of guanine phosphoribosyltransferase (K(i) 4.7 mum) and hypoxanthine phosphoribosyltransferase (K(i) 8.3 mum). Hypoxanthine is a competitive inhibitor of guanine phosphoribosyltransferase (K(i) 3.4 mum). 4. Differences in kinetic parameters and in the distribution of phosphoribosyltransferase activities after electrophoresis in starch gel indicate that different enzymes are involved in the conversion of adenine, guanine and hypoxanthine into their nucleotides. 5. From the low values of K(i) for 6-mercaptopurine, and from published evidence that ascites-tumour cells require supplies of purines from the host tissues, it is likely that inhibition of hypoxanthine and guanine phosphoribosyltransferases by free 6-mercaptopurine is involved in the biological activity of this drug.

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Inhibition of purine phosphoribosyltransferases from Ehrlich ascites-tumour cells by purine nucleotides.

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| S-EPMC1265200 | biostudies-other

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