Physicochemical and catalytic Properties of NAD<sup>+</sup>-Dependent Malate Dehydrogenase Isoforms from maize Mesophyll
Malate dehyrogenase isoforms (46- and 70-fold purifications) with specific activities of the 640 and 990 U/mg protein were obtained in an electrophoretically homogeneous state from maize mesophyll. The physicochemical and catalytic properties of these isoforms were studied. The molecular weight and the Michaelis constants were determined; the effect of hydrogen ions on the forward and reverse MDH reaction was studied. The results of SDS-PAGE demonstrated that malate dehydrogenase isoforms have an oligomeric structure comprised of identical subunits. The first isoform with a molecular weight of 126.58 kDa is tetramer, and the second isoform with a molecular weight of 63.3 is dimer.  Keywords: malate dehydrogenase, isoforms, Zea mays, mesophyll, purification, subunit structure, the M-ichaelis constant, electrophoresis