2-Hydroxymuconate semialdehyde is formed from catechol by the enzyme catechol 2,3-dioxygenase during the degradation of benzoates.
It is oxidised to (2E,4Z)-2-hydroxymuconic acid] by the enzyme 2-hydroxymuconate-6-semialdehyde dehydrogenase.
It is also degraded into formate and 2-oxopent-4-enoic acid by 2-hydroxymuconate-semialdehyde hydrolase.