Activities of key enzymes in relation to glucose flux in tumor-host livers.

1. Isotope and non-isotope methods were used to study hepatic metabolism of glucose in tumor-host livers. 2. Glycogen synthase, phosphofructokinase activities (Vmax) were decreased, while glucose-6-phosphate dehydrogenase and lactate dehydrogenase activities were increased in tumor-host livers. 3. Glycogen phosphorylase, glucokinase and several mitochondrial enzymes, had normal maximum activity in tumor-host livers. Net flux of glucose was decreased in the Embden-Meyerhof and the pentose phosphate pathway in tumor animals. 4. The hepatic cycling of glucose-carbons in tumor animals was significantly decreased as shown by different [14C] [3H] ratios of radioactivity in RNA and lactate, determined from simultaneous incorporation of [U-14C]glucose and [2-3H]glucose. 5. This study demonstrates that previous reports of increased activities of rate limiting enzymes of glucose metabolism in tumor-host livers do not represent a general finding of high glucose metabolism in tumor-host livers.