NADP malic Enzyme from Sugarcane Leaves: Kinetic Properties of Its Different Oligomeric Structures

A.A. IGLESIAS, C.S. ANDREO

EUROPEAN JOURNAL OF BIOCHEMISTRY

Año: 1990 vol. 192 p. 729 - 733

0014-2956

NADP-dependent malate dehydrogenase (decarboxylating) from sugar cane leaves was inhibited by increasingthe ionic strength in the assay medium. The inhibitory effect was higher at pH 7.0 than 8.0, with median inhibitoryconcentrations (ICs0) of 89 mM and 160 mM respectively, for inhibition by NaCl. Gel-filtration experimentsindicated that the enzyme dissociated into dimers and monomers when exposed to high ionic strength (0.3 MNaCl). By using the enzyme-dilution approach in the absence and presence of 0.3 M NaC1, the kinetic propertiesof each oligomeric species of the protein was determined at pH 7.0 and 8.0. Tetrameric, dimeric and monomericstructures were shown to be active but with different V and K, values. The catalytic efficiency of the oligomerswas tetramer > dimer > monomer, and each quaternary structure exhibited higher activity at pH 8.0 than 7.0.Dissociation constants for the equilibria between the different oligomeric forms of the enzyme were determined.It was established that Kd values were affected by pH and Mg2+ levels in the medium. Results suggest that thedistinct catalytic properties of the different oligomeric forms of NADP-dependent malate dehydrogenase andchanges in their equilibrium could be the molecular basis for an efficient physiological regulation of thedecarboxylation step of C4 metabolism.