M. MacDonald, H. Lardy
Apr 10, 1978
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0
Influential Citations
21
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Journal
The Journal of biological chemistry
Abstract
3-Aminopicolinate, a metal-chelating agent and a hyperglycemic agent in the rat, permits FeS+ to increase the maximal velocity of purified rat liver cytosolic P-enolpyruvate carboxykinase greater than 3-fold and also enhances activation by Mn”+ when it is incubated with metal ion and the enzyme prior to assaying for activity in the forward or reverse direction. In the presence or absence of added metal ion, 3-aminopicolinate does not alter the Michaelis constant of the enzyme for oxalacetate or MgITP. In the absence of added divalent transition metal ions, it has no effect upon enzyme activity indicating that it is not activating by removal of an inhibitory metal from the enzyme. 3-Aminopicolinate also permits Fe2+ to activate the enzyme in the presence of inhibitory concentrations of inorganic phosphate. Maximal activation is sustained during 5 h of incubation. Thus, 3-aminopicolinate may serve as a model for ferroactivator, a naturally occurring protein which permits Fe2+ to activate the enzyme in uitro. Maximal activation of the enzyme is obtained by incubation with 100 FM or greater metal ion. The concentrations of Fe2+ and iVInY+ in the incubation mixture that activate the enzyme half-maximally (K,,.,) are 20 and 17 PM, respectively. The K,,., of 3aminopicolinate in the incubation mixture ranges between 20 and 50 PM and appears to increase with increasing concentration of Fe2+ or Mn’+. Quinolinate and 3-mercaptopicolinate have previously been reported to be moderately strong and strong inhibitors, respectively, of P-enolpyruvate carboxykinase. 3-Mercaptopicolinate is a more potent inhibitor of the enzyme when it has been incubated with Fez+ with or without 3-aminopicolinate than when it has been incubated with Mn’+ or not incubated with a metal ion. Quinolinate inhibits significantly only when the enzyme has been activated by Fe” and 3-aminopicolinate; it moderately enhances activation of the enzyme by Mn”+. The degree of quenching of the electron paramagnetic resonance signal of Mn’+ by the three pyridine carboxylic acids was used to estimate their affinities for Mn’+. The