Fructose 1,6-diphosphatase of mouse Ehrlich ascites tumor and its comparison with the enzymes of liver and skeletal muscle of the mouse

Evidence is presented which suggests that, during the lag period, the fructose diphosphatase is inhibited by AMP present in the extracts, and the tumor enzyme resembles the muscle enzyme rather than the liver enzyme.

Abstract

1. The enzyme fructose 1,6-diphosphatase (d-fructose-1,6-diphosphate I-phosphohydrolase, EC 3.1.3.11) has been identified in extracts of mouse Ehrlich ascites carcinoma. The tumor cells have higher activity than mouse skeletal muscle. Fructose diphosphatase was partially purified from mouse Ehrlich ascites tumor, liver and leg muscle. 2. The partially purified Ehrlich ascites tumor fructose diphosphatase is inhibited by substrate concentrations greater than 0.05 mM. At non-inhibitory concentrations of substrate, a Km of 8.1·10−6M was measured. At 0.1 mM Fru-1,6-P2, the optimum pH is 7.4 and at this pH maximum activity requires Mg2+ (or Mn2+) and EDTA. These properties are similar to those of fructose diphosphatase from rat liver. 3. Like fructose diphosphatase identified in other tissues, the tumor enzyme is inhibited by AMP. At pH 7.4 and with 0.1 mM Fru-1,6-P2, 50% inhibition requires 1.3 μM AMP. The corresponding values for the enzymes from mouse liver and leg muscle are 130 and 2.1 μM, respectively. Therefore, regarding the sensitivity to inhibition by AMP, the tumor enzyme resembles the muscle enzyme rather than the liver enzyme. 4. With tumor extracts, but not with liver or muscle extracts, a lag period of about 10 min was observed in the assay measurement of fructose diphosphatase. Evidence is presented which suggests that, during the lag period, the fructose diphosphatase is inhibited by AMP present in the extracts.