Regulation of glycolysis in sea bass liver: phosphofructokinase isozymes

Sea bass (Dicentrarchus labrax L.) liver phosphofructokinase (PFK) presents biphasic kinetics with respect to fructose-6-phosphate (F-6-P) in experiments carried out with crude extract. After the enzyme had been purified, two isozymes have been detected after chromatographic treatment. The two isozymes present different kinetic behaviour PFK-L1, the first eluted phosphofructokinase activity shows positive cooperativity with respect to fructose-6-phosphate and PFK-L2, the second activity fraction, has a Hill coefficient of 0.38 (negative cooperativity). The first isozyme shows less affinity for fructose-6-phosphate than that shown by PFK-L2. The joint kinetics of both isozymes produces a biphasic kinetics with respect to fructose-6-phosphate, similar to that observed in crude extracts.