fenylpropanoidvägen

The phenylpropanoid pathway is a fundamental metabolic route found in plants. It is responsible for the biosynthesis of a vast array of secondary metabolites, including lignin, flavonoids, stilbenoids, and phenolic acids. The pathway begins with the amino acid phenylalanine or tyrosine, which are derived from the shikimate pathway.

The first committed step in the phenylpropanoid pathway is the deamination of phenylalanine or tyrosine by phenylalanine ammonia-lyase (PAL) or tyrosine ammonia-lyase (TAL), respectively. This reaction produces cinnamic acid or p-coumaric acid. These cinnamic acid derivatives are then further modified through a series of enzymatic steps, including hydroxylation, methylation, and conjugation.

Key intermediates in the pathway include p-coumaroyl-CoA, caffeoyl-CoA, and feruloyl-CoA. These activated thioesters serve as substrates for various downstream enzymes. For instance, p-coumaroyl-CoA is a precursor to chalcones, which are then converted into flavonoids, a diverse group of compounds involved in UV protection, pigment production, and defense against pathogens.

Lignin, a complex polymer that provides structural support to plant cell walls, is synthesized from p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol, which are derived from the phenylpropanoid pathway. Additionally, phenolic acids, such as caffeic acid and ferulic acid, are produced and can be further conjugated or incorporated into other molecules.

The phenylpropanoid pathway is crucial for plant survival and plays significant roles in plant development, adaptation to environmental stresses, and defense mechanisms. The diverse products of this pathway have also found numerous applications in human society, including pharmaceuticals, food additives, and industrial materials.