On the Molecular Mechanism of Maize Phosphoenolpyruvate Carboxylase Activation by Thiol Compounds

A.A. IGLESIAS, C.S. ANDREO

PLANT PHYSIOLOGY.

Año: 1984 vol. 75 p. 983 - 987

0032-0889

Incubation of purified phosphoenolpyruvate carboxylase from Zcamays L. leaves with dithiothreitol resulted in an almost 2-fold increasein the enzymic activity. The activated enzyme showed the same affinityfor its substrates and the same sensitivity with respect to malate andoxalacetate inhibition. The activation induced by dithiothreitol was reversedby diamide, an oxidant of vicinal dithiols, suggesting that theredox state of disulfide bonds of the enzyme may be important in theexpression of the maximal catalytic activity.Titration of thiol groups before and after activation of maize phosphoenolpyruvatecarboxylase by dithiothreitol shows an increase of theaccessible groups from 8 to 12 suggesting that the reduction of twodisulfide bonds accompanied the activation. The thiols exposed by thetreatment with dithiothreitol were available to reagents in nondenaturedenzyme and two of them were reoxidized to a disulfide bond by diamide.It is concluded that the mechanism of phosphoenolpyruvate carboxylseactivation by dithiothreitol involves the net reduction of two disulfidebonds in the enzyme.