Non homologous isofunctional enzymes

A non-homologous isofunctional enzyme (NISE) is analogous in function to a known enzyme, but share unique protein sequence or folding (Omelchenko et al., 2010). As such, there may be confusion regarding the Enzyme Commission number system.

A recent example is of the enzyme urate hydroxylase (EC 1.14.13.113) which catalyzes the decomposition of urate, an important constituent of nitrogen cycling. The newly discovered HpyO gene was non-homologous in sequence to the original gene HpxO (O'leary et al., 2009) but yet shared certain characteristics enabling it to perform a similar reaction (Michiel et al., 2012).