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

摘要

1. Certain enzymes concerned with citrate and glucose metabolism have been measured in two transplanted rat hepatomas, one induced with ethionine (minimal deviation type) and one induced with dimethylaminoazobenzene. In these hepatomas both citrate-cleavage enzyme and NADP-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 tumours and depressed rate of fatty acid synthesis. 2. The glucose–ATP-phosphotransferase activity was below normal liver values in the ethionine-induced tumour but greater than normal in the dimethylaminoazobenzene-induced hepatoma. The apparent Km values for the glucose–ATP phosphotransferases of these hepatomas were approx. 8×10−5m; no evidence was found for an enzyme with a high Km for glucose equivalent to liver glucokinase. 3. Of the enzymes of the pentose phosphate pathway, glucose 6-phosphate-dehydrogenase activity was three to five times as great whereas 6-phosphogluconate-dehydrogenase activity was the same or lower than normal liver in the ethionine-and dimethylaminoazobenzene-induced tumours respectively.