title: Regulation of glycolysis in Neurospora crassa. Kinetic properties of pyruvate kinase.
abstract: Pyruvate kinase (ATP:pyruvate phosphotransferase, EC 2.7.1.40), extracted from the mycelium of Neurospora crassa has been purified 560-fold by precipitation with ammonium sulphate, chromatography with DEAE-Sephadex, and gel filtration with Sephadex G-200. Potassium and magnesium are required for enzyme activity. Fructose, 1,6-diphosphate is the only physiological activator found for the enzyme. In decreasing order of potency, citrate, oxalacetate, calcium, and ATP are inhibitors. Phosphoenolpyruvate is cooperatively bound by the enzyme and the cooperatively is reduced by ATP and completely eliminated by fructose-1,6-diphosphate. Lowering of pH from 7-5 to 5-5 changes the Hill coefficient from 2-7 to 1-0. Substitution of ADP by other nucleotides reduces enzyme activity. Manganese can substitute for the cofactor magnesium, but the reaction velocity is then reduced. MgADP- is cooperatively bound by the enzyme and inhibition of the enzyme occurs only when either magnesium or ADP is in excess of the other beyond the optimum concentration. These kinetics properties of pyruvate kinase are compatible with the role of a regulator of glycolysis in Neurospora crassa.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002474:Cell-Free System; D002951:Citrates / Q000494:pharmacology; D004789:Enzyme Activation; D005636:Fructosephosphates / Q000494:pharmacology; D006019:Glycolysis; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D009491:Neurospora / Q000378:metabolism*; D009492:Neurospora crassa / Q000201:enzymology / Q000378:metabolism*; D010071:Oxaloacetates / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011770:Pyruvate Kinase / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D002951:Citrates; D005636:Fructosephosphates; D010071:Oxaloacetates; D000255:Adenosine Triphosphate; D011770:Pyruvate Kinase; D008274:Magnesium; D011188:Potassium; D002118:Calcium