Activities of some enzymes concerned with citrate and glucose metabolism in transplanted rat hepatomas

Abstract

Certain enzymes concerned with citrate and glucose metabolism have been measured in 2 transplanted rat hepatomas, one induced with ethionine (minimal deviation type) and one induced with dimethylaminoazobenzene. In these hepatomas both citrate-cleavage enzyme and NADP (triphosphopyridine nucleotide)-linked isocitrate dehydrogenase in the soluble fraction of the cell were approximately one-third of the values for normal rat liver. These changes have been discussed in relation to the increased citric acid content of tumors and depressed rate of fatty acid synthesis. The glucose-ATP (adenosine triphosphate)-phosphotransferase activity was below normal liver values in the ethionine-induced tumor but greater than normal in the dimethylaminoazobenzene-induced hepatoma. The apparent km values for the glucose[long dash]ATP phosphotransferases of these hepatomas were approximately 8 x 10-5 M; no evidence was found for an enzyme with a high Km for glucose equivalent to liver gluco-kinase. Of the enzymes of the pentose phosphate pathway, glucose 6-phosphate-dehydrogenase activity was 3 to 5 times as great whereas 6-phosphogluconatedehydrogenase activity was the same or lower than normal liver in the ethionine-and dimethylaminoazobenzene-induced tumors respectively.