Protease recognition occurs via recognition loops in the two domains. The recognition loops of the first domain are unaffected by the second domain, but those of the second domain are close to the first domain. The first domain could interfere with protease binding at the second. This selective inhibition may prove to be a useful regulatory mechanism. These enzymes form part of the C 4 pathway of photosynthesis in monocot plants such as maize and the dicot plants such as Flaveria bidentis .
Light activation comes about by the photosynthetic dependent reduction of disulphide bonds.
The purified oxidised enzyme from F. bidentis is inactive but can be activated many thousand-fold by thiol reducing. This regulatory mechanism is similar to the covalent regulation by protein phosphorylation that occurs in other organisms. The extensions contain cysteines that form the regulatory disulphides. The molecular basis for the dramatic change in activity between oxidised and reduced NADP-malate dehydrogenase is not well understood. A schematic representation of plant malate dehydrogenase.