Vanadyl(IV) complexes with pyruvate kinase: activation of the enzyme and electron paramagnetic resonance properties of ternary complexes with the protein.
Complexes of the oxocation of vanadyl(IV), VO2+, with pyruvate kinase from rabbit muscle have been investigated by steady-state kinetic assays and by EPR spectroscopy. Pyruvate kinase requires 2 eq of divalent cation for activity. VO2+ alone is a poor activator of the normal physiological reaction catalyzed by the enzyme and of the enzyme-catalyzed exchange of the methyl protons of pyruvate with solvent. VO2+ alone is, however, an activator of the enzyme-catalyzed phosphorylation of glycolate by ATP. VO2+ is more effective than Mg2+ in activation of the bicarbonate-dependent ATPase reaction of pyruvate kinase, and in the enzyme-catalyzed hydrolysis of phosphoenolpyruvate. EPR data show that VO2+ binds to the divalent cation site on the protein competitively with respect to Mg2+. The VO2+-enzyme complex has a high affinity for bicarbonate. Direct coordination of pyruvate, oxalate, and glycolate to the enzyme-bound VO2+ has been established by EPR measurements with specifically 17O-labeled forms of these compounds.
Lord
K A
KA
Institute for Enzyme Research, Graduate School, University of Wisconsin, Madison 53705.
Reed
G H
GH
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D004578:Electron Spin Resonance Spectroscopy; D004789:Enzyme Activation / Q000187:drug effects; D008274:Magnesium / Q000378:metabolism; D011770:Pyruvate Kinase / Q000378:metabolism*; D011817:Rabbits; D014638:Vanadates / Q000378:metabolism / Q000494:pharmacology*
D014638:Vanadates; D000255:Adenosine Triphosphate; D011770:Pyruvate Kinase; D008274:Magnesium