title: A steady-state kinetic analysis of the fructose 1,6-bisphosphate-activated pyruvate kinase from Carcinus maenas hepatopancreas.
abstract: 1. An investigation of the reaction mechanism of the fructose 1,6-bisphosphate-activated pyruvate kinase isolated from the hepatopancreas of the crab Carcinus maenas was conducted. The enzyme was assayed in the presence of 500 microns-fructose 1,6-bisphosphate, 75 mM-KCl and 8 mM-Mg2+free at 25 degrees C. The results are consistent with a rapid-equilibrium random mechanism. 2. Evidence is presented that suggests the formation of two mixed-substrate-product dead-end complexes, enzyme-ADP-pyruvate and enzyme-ADP-ATP. 3. Competitive substrate inhibition was observed for both substrates, ADP and phosphoenolpyruvate, suggesting the formation of the complexes enzyme-ADP-ADP and enzyme-phosphoenolpyruvate-phosphoenolpyruvate in the suggested mechanism. 4. Data from the ATP product-inhibition studies indicate the formation of the complex enzyme-ATP-ATP. This suggests that in the reverse reaction ATP also will show substrate inhibition. 5. The presence of a saturating concentration of fructose 1,6-bisphosphate does not cause full activation of the purified preparations of the enzyme. 6. Pyruvate kinase activity in the supernatant of a hepatopancreas homogenate was completely activated by fructose 1,6-bisphosphate, suggesting that the binding of this ligand to the purified pyruvate kinase was impaired.
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D003386:Brachyura / Q000201:enzymology*; D004789:Enzyme Activation / Q000187:drug effects; D005635:Fructosediphosphates / Q000494:pharmacology*; D006598:Hexosediphosphates / Q000494:pharmacology*; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008954:Models, Biological; D010179:Pancreas / Q000201:enzymology; D010728:Phosphoenolpyruvate / Q000378:metabolism; D011770:Pyruvate Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011773:Pyruvates / Q000494:pharmacology
chemical_list: D005635:Fructosediphosphates; D006598:Hexosediphosphates; D011773:Pyruvates; D000244:Adenosine Diphosphate; D010728:Phosphoenolpyruvate; D000255:Adenosine Triphosphate; D011770:Pyruvate Kinase