Evolution and Structure
In most organisms, malate dehydrogenase exists as a homodimeric molecule and is closely related to lactate dehydrogenase in structure. It is a large protein molecule with subunits weighing between 30 and 35 kDa. Based on the amino acid sequences, it seems that MDH has diverged into two main phylogenetic groups that closely resemble either mitochondrial isozymes or cytoplasmic/chloroplast isozymes. Because the sequence identity of malate dehydrogenase in the mitochondria is more closely related to its prokaryotic ancestors in comparison to the cytoplasmic isozyme, the theory that mitochondria and chloroplasts were developed through endosymbiosis is plausible. It is interesting to note that the amino acid sequences of archaeal MDH are more similar to that of LDH than that of MDH of other organisms. This indicates that there is a possible evolutionary linkage between lactate dehydrogenase and malate dehydrogenase.
Each subunit of the malate dehydrogenase dimer has two distinct domains that vary in structure and functionality. A parallel β-sheet structure makes up the domain, while four β-sheets and one α-helix comprise the central NAD+ binding site. The subunits are held together through extensive hydrogen-bonding and hydrophobic interactions.
Read more about this topic: Malate Dehydrogenase
Famous quotes containing the words evolution and/or structure:
“Historians will have to face the fact that natural selection determined the evolution of cultures in the same manner as it did that of species.”
—Konrad Lorenz (1903–1989)
“The philosopher believes that the value of his philosophy lies in its totality, in its structure: posterity discovers it in the stones with which he built and with which other structures are subsequently built that are frequently better—and so, in the fact that that structure can be demolished and yet still possess value as material.”
—Friedrich Nietzsche (1844–1900)