Abstract:

Two electrophoresis-pure isoenzymes (c-MDH and m-MDH) of malate dehydrogenase from duck heart were
obtained through the procedures including homogenization, ammonium sulfate precipitation, organic solvent precipitation,
DEAE-sepharose chromatography and Superdex-200 gel filtration. c-MDH present in the crude enzyme solution in a higher
amount was characterized. The results showed that the purity of c-MDH and m-MDH were increased by 69.07- and 130.40-
fold with activity recoveries of 25.54% and 10.98%, respectively. The molecular mass of the subunits in c-MDH and m-MDH
were 39.58 ku and 37.62 ku, respectively. Enzymatic characterization showed that the optimal reaction temperature and pH
for c-MDH were 55 ℃ and 7.2, respectively, and it was stable below 30 ℃ and at pH 6－9. Meanwhile, its Km using oxobutanedioic
acid as the substrate was 140.93 mmol/L. The enzyme activity could be strongly inhibited by oxalic acid, SDS,
Cu2+, Co2+ and Ag+, while it could be obviously activated by Mg2+, K+, and Ba2+.

Key words: duck heart, malate dehydrogenase (MDH), isolation and purification, characterization