FIGURE 2.

Enzyme evolution toward higher specificity, retaining some substrate and reaction ambiguity. Shown is a schematic diagram of the origin of metabolome diversity between species and within species (adapted from Ref. 1). Given the currently accepted model of enzyme evolution by gene duplication and subsequent specialization, a generalist progenitor enzyme may have performed catalytic reactions (a and b) on substrates (A, B, and C). The phylogenetic tree for this enzyme may have led to isoenzymes that accept only substrate B for reaction a, whereas others retained some level of substrate and reaction ambiguity, leading to higher metabolome diversity (e.g. adding reaction a to substrate C or accepting the novel substrate D for reactions a and b).