Horseradish peroxidase and related secretory plant peroxidases. Secretory peroxidases belong to class III of the plant heme-dependent peroxidase superfamily. All members of the superfamily share a heme prosthetic group and catalyze a multistep oxidative reaction involving hydrogen peroxide as the electron acceptor. Class III peroxidases are found in the extracellular space or in the vacuole in plants where they have been implicated in hydrogen peroxide detoxification, auxin catabolism and lignin biosynthesis, and stress response. Class III peroxidases contain four conserved disulphide bridges and two conserved calcium binding sites.

4-coumarate--CoA ligase

Firefly luciferase of light emitting insects and 4-Coumarate-CoA Ligase (4CL). This family contains two functionally unique groups of proteins; one group is insect firefly luciferases and the other is plant 4-coumarate:coenzyme A ligases. However, they share significant sequence similarity in spite of their functional diversity. Luciferase catalyzes the production of light in the presence of MgATP, molecular oxygen, and luciferin. In the first step, luciferin is activated by acylation of its carboxylate group with ATP, resulting in an enzyme-bound luciferyl adenylate. In the second step, luciferyl adenylate reacts with molecular oxygen, producing an enzyme-bound excited state product (Luc=O*) and releasing AMP. This excited-state product then decays to the ground state (Luc=O), emitting a quantum of visible light. 4-coumarate:coenzyme A ligase is a key enzyme in the phenylpropanoid metabolic pathway for monolignol and flavonoid biosynthesis. It catalyzes the synthesis of hydroxycinnamate-CoA thioesters in a two-step reaction, involving the formation of hydroxycinnamate-AMP anhydride and then the nucleophilic substitution of AMP by CoA. The phenylpropanoid pathway is one of the most important secondary metabolism pathways in plants and hydroxycinnamate-CoA thioesters are the precursors of lignin and other important phenylpropanoids.

4-coumarate--CoA ligase-like

4-Coumarate-CoA Ligase (4CL). 4-Coumarate:coenzyme A ligase is a key enzyme in the phenylpropanoid metabolic pathway for monolignol and flavonoid biosynthesis. It catalyzes the synthesis of hydroxycinnamate-CoA thioesters in a two-step reaction, involving the formation of hydroxycinnamate-AMP anhydride and the nucleophilic substitution of AMP by CoA. The phenylpropanoid pathway is one of the most important secondary metabolism pathways in plants and hydroxycinnamate-CoA thioesters are the precursors of lignin and other important phenylpropanoids.