title: Kinetic properties of cerebral pyruvate kinase.
abstract: Partly purified guinea-pig brain pyruvate kinase is not activated by fructose 1,6-diphosphate and gives hyperbolic substrate-saturation curves with phosphoenolpyruvate. It is therefore different from the L-type pyruvate kinase of mammalian liver. Inhibition by MgATP(2-) was competitive for MgADP(-) but not for phosphoenolpyruvate, and the enzyme is therefore different from the M-type pyruvate kinase, which is said to be competitively inhibited by MgATP(2-) with respect to both substrates. The K(i)(MgATP(2-)) value of approx. 8mm for the brain enzyme is higher than the values (about 2mm) reported for the muscle enzyme. Stimulation of enzymic activity was observed at low (1-2mm) concentrations of MgATP(2-). Substrate kinetic constants were K(m) (MgADP(-))=0.47mm, K(m) (phosphoenolpyruvate)=0.08mm. Free Mg(2+) at very high concentrations (over 10mm) was inhibitory (K(i)=20-32mm). Neither ADP(3-) nor 5'-AMP(2-) inhibited the activity. The brain enzyme was concluded to be different from both the M-type and the L-type of other mammalian organs such as muscle and liver.
mesh_terms: D000244:Adenosine Diphosphate; D000249:Adenosine Monophosphate; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000201:enzymology*; D002498:Centrifugation; D003201:Computers; D005636:Fructosephosphates / Q000378:metabolism; D006168:Guinea Pigs; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008274:Magnesium / Q000494:pharmacology; D009132:Muscles / Q000378:metabolism; D010728:Phosphoenolpyruvate / Q000378:metabolism; D011770:Pyruvate Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013053:Spectrophotometry
chemical_list: D005636:Fructosephosphates; D000249:Adenosine Monophosphate; D000244:Adenosine Diphosphate; D010728:Phosphoenolpyruvate; D000255:Adenosine Triphosphate; D011770:Pyruvate Kinase; D008274:Magnesium