Issues

The polyamine biosynthetic enzyme arginine decarboxylase has emerged multiple times from different proteins folds by convergent evolution, and has also emerged independently, at different times, from the same protein fold by pseudoconvergent evolution. In some cases, the enzyme cofactor is an internally produced pyruvoyl group, in others it is pyridoxal 5'-phosphate. The origin of this enzyme from such diverse structural classes and with different catalytic mechanisms indicates that the emergence of polyamine biosynthesis on Earth was, and is, inevitable. For more information, please see review article, “Evolution of Biosynthetic Diversity” by Anthony J. Michael, pages 2277–2299.