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4-Hydroxyphenylpyruvic acid (4-HPPA) is an intermediate in the metabolism of the amino acid phenylalanine. The aromatic side chain of phenylalanine is hydroxylated by the enzyme phenylalanine hydroxylase to form tyrosine. The conversion from tyrosine to 4-HPPA is in turn catalyzed by tyrosine aminotransferase. [2]
These enzymes primarily hydroxylate the amino acids L-phenylalanine, L-tyrosine, and L-tryptophan, respectively. The AAAH enzymes are functionally and structurally related proteins which act as rate-limiting catalysts for important metabolic pathways. [1]
In plants, the shikimate pathway first leads to the formation of chorismate, which is the precursor of phenylalanine, tyrosine, and tryptophan.These aromatic amino acids are the precursors of many secondary metabolites, all essential to a plant's biological functions, such as the hormones salicylate and auxin.
The pathway starts with two substrates, phosphoenol pyruvate and erythrose-4-phosphate, and ends with chorismate (chrorismic acid), a substrate for the three aromatic amino acids. The fifth enzyme involved is the shikimate kinase , an enzyme that catalyzes the ATP -dependent phosphorylation of shikimate to form shikimate 3-phosphate (shown in ...
Phenylalanine hydroxylase (PAH) (EC 1.14.16.1) is an enzyme that catalyzes the hydroxylation of the aromatic side-chain of phenylalanine to generate tyrosine.PAH is one of three members of the biopterin-dependent aromatic amino acid hydroxylases, a class of monooxygenase that uses tetrahydrobiopterin (BH 4, a pteridine cofactor) and a non-heme iron for catalysis.
In plants, all phenylpropanoids are derived from the amino acids phenylalanine and tyrosine. Phenylalanine ammonia-lyase (PAL, a.k.a. phenylalanine/tyrosine ammonia-lyase) is an enzyme that transforms L-phenylalanine and tyrosine into trans-cinnamic acid and p-coumaric acid, respectively.
Phenylalanine is a precursor for tyrosine, the monoamine neurotransmitters dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline), and the biological pigment melanin. It is encoded by the messenger RNA codons UUU and UUC. Phenylalanine is found naturally in the milk of mammals.
HGD appears in the metabolic pathway of tyrosine and phenylalanine degradation once the molecule homogentisate is produced. Homogentisate reacts with HGD to produce maleylacetoacetate, which then is further used in the metabolic pathway. HGD requires the use of Fe 2+ and O 2 in order to cleave the aromatic ring of homogentisate. [2]