malate dehydrogenase

Malate dehydrogenase (MDH) is one of the key enzymes in glycometabolism, which can catalyze the reversible conversion between malic acid and oxaloacetic acid. MDHS play an important role in many physiological activities of cells, including energy metabolism of mitochondria and active oxygen metabolism of plants.

Biochemical characteristics of malate dehydrogenase

Optimum pH and temperature

The optimum pH value of MDHS was about 8.0. For example, the enzyme activity of Streptomyces and Escherichia coli was the highest at pH 8.1. The optimum reaction temperature was 40 ~ 65 ℃. For example, the optimum temperature of MDH of Bacillus subtilis and myocardial MDH of pig is about 50 ℃, and the stability of Bacillus stearothermophilus (bmdh) is better at 65 ℃. The MDHS activity of most species is not high when the temperature tends to the two poles. However, the MDH from psychrophilic bacteria (aamdh) remains high at about 4 ℃, and that of thermophilic bacteria can remain about 1 h at 90 ℃. This difference may be due to the preference of some residues in the active site, the distribution of the charge of substrate and cofactor, and the interaction of ion pairs between subunits It is caused by the function and other reasons.

thermal stability

The thermal stability of ecmdh and Bacillus subtilis MDH was poor. Bacillus stearothermophilus bsmdh is quite stable at high temperature. It is speculated that the number of hydrogen bonds, the number and position of proline or glycase molecules and their interaction are related to the thermophilic bacteria aamdh. Glycerol is the best stabilizer to maintain the activity of MDHS at low temperature, while cyclopolyol and sorbitol can maintain the activity of MDHS at high temperature. The stability principle may be the interaction between hydroxyl groups and enzyme molecules, or alcohols reduce the dielectric constant of the medium and strengthen the hydrophobic interaction of enzyme molecules, which makes the enzyme eggs less affected by water molecules.

Influence of metal ions

The results showed that K + could activate MDH, Mg2 + and Ca2 + had little effect on enzyme activity; Zn2 +, P2 + and Cu2 + had different degrees of inhibition on enzyme activity, among which Cu2 + had the strongest inhibition, and 97% of enzyme activity was inhibited when its concentration was 1m.

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