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Structural requirements for pyridinecarboxylate effects on phosphoenol pyruvate carboxy kinase


, : Structural requirements for pyridinecarboxylate effects on phosphoenol pyruvate carboxy kinase. Bioorganic Chemistry 7(2): 251-262

It was previously established that quinolinic acid and 3-mercaptopicolinic acid cause hypoglycemia by inhibiting phosphoenolpyruvate (PEP) carboxykinase and gluconeogenesis. In the rat, 3-aminopicolinic acid permits Fe2+ to activate this enzyme; it enhances gluconeogenesis and causes hyperglycemia. In the present study, other pyridine carboxylates were screened for effects on the activity of PEP carboxykinase. The structural requirement for an inhibitor or an activator of this enzyme was defined: it must be a picolonic acid derivative with the .alpha.-carboxyl unsubstituted and with another group on position 3. The group at position 3 determines the effect (inhibition or activation) and the potency of the compound. Compounds such as picolinic acid, all the isomers of quinolinic acid, 2-mercaptonicotinic acid and 2-aminonicotinic acid were inactive. Fe2+ enhances the potency of quinolinate and 2-mercaptopicolinate 15- to 20-fold, and 3-aminopicolinate does not activate the carboxykinase in the absence of Fe2+. It is therefore assumed that Fe2+ binds to the ring N and the .alpha.-carboxyl group of one or more molecules of these compounds to form an effective coordination complex. Complexes involving picolinate derivatives with an acidic function at position 3 inhibit; the complex of Fe2+ with 3-aminopicolinate either delivers Fe2+ to the catalytic site and then dissociates or the Fe2+ in the complex is catalytically active. 3-Aminopicolinate causes hyperglycemia in the guinea pig. It activates guinea pig liver cytosolic PEP carboxykinase in vitro but does not activate the mitochondrial carboxykinase. If activation of PEP carboxykinase is the means by which 3-aminopicolinate causes hyperglycemia, the findings indicate that the cytosolic enzyme can play an important role in glucose synthesis in species having appreciable amounts of both carboxykinases.

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