Structural, immunological and kinetic comparisons of NADP-dependent malate dehydrogenases from spinach (C3) and corn...

This paper compares structural, immunological and kinetic properties of corn (C4) and spinach (C3) NADP-malate dehydrogenases. These chloroplastic enzymes are regulated in vivo by thiol-disulfide interchange. Both in their oxidized (inactive) and reduced (active) states these enzymes have a dimeric structure with molecular masses for the subunit ranging from 28 kDa to 38 kDa according to the procedure used for the determination. These enzymes are thus structurally related. The use of specific antibodies showed that they are also immunologically related although not identical. Finally both enzymes showed close kinetic properties with comparable kcat and Km. Since C4 plants have approximately ten times more NADP-malate dehydrogenase activity than C3 plants, these data suggest that the differences in activities are probably related to the enzyme content of each plant type.