INDUCTION OF GLYOXYLATE CYCLE ENZYMES IN RAT-LIVER UPON FOOD STARVATION

The key enzymes of the glyoxylate cycle, isocitrate lyase and malate s ynthase, have been detected in liver of food-starved rats. Activities became measurable 3 days and peaked 5 days after the beginning of star vation, Both enzymes were found in the peroxisomal cell fraction after organelle fractionation by isopycnic centrifugation. Isocitrate lyase was purified 112-fold by ammonium sulfate precipitation, and chromoto graphy on DEAE-cellulose and Toyopearl HW-65. The specific activity of the purified enzyme was 9.0 units per mg protein, The K-m(isocitrate) was 68 mu M and the pH optimum was at pH 7.4. Malate synthase was enr iched I-fold by ammonium sulfate precipitation. The enzyme had a K-m(a cetyl-CoA) of 0.2 mu M, a K-m(glyoxylate) of 3 mM and a pH optimum of 7.6.