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Alloenzymes (or also calledallozymes) are variant forms of anenzyme which differ structurally but not functionally from other allozymes coded for by differentalleles at the samelocus. These are opposed toisozymes, which are enzymes that perform the same function, but which are coded by genes located at different loci.[1]
Alloenzymes are common biologicalenzymes that exhibit high levels of functionalevolutionary conservation throughout specificphyla andkingdoms. They are used byphylogeneticists as molecular markers to gauge evolutionary histories and relationships between different species. This can be done because allozymes do not have the same structure. They can be separated bycapillary electrophoresis. However, some species are monomorphic for many of their allozymes which would make it difficult for phylogeneticists to assess the evolutionary histories of these species.[2] In these instances, phylogeneticists would have to use another method to determine the evolutionary history of a species.
These enzymes generally perform very basic functions found commonly throughout all lifeforms, such asDNA polymerase, the enzyme that repairs and copiesDNA. Significant changes in this enzyme reflect significant events in evolutionary history of organisms. As expected DNA polymerase shows relatively small differences in itsamino acid sequence between phyla and even kingdoms.
The key to choosing which alloenzyme to use in a comparison between multiple species is to choose one that is as variable as possible while still being present in all the organisms. By comparing the amino acid sequence of the enzyme in the species, more amino acid similarities should be seen in species that are more closely related, and fewer between those that are more distantly related. The less well conserved the enzyme is, the more amino acid differences will be present in even closely related species.[3]