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Tyrosine ball and stick model spinning. L-Tyrosine or tyrosine (symbol Tyr or Y) [2] or 4-hydroxyphenylalanine is one of the 20 standard amino acids that are used by cells to synthesize proteins. It is a conditionally essential amino acid with a polar side group.
Tyrosine hydroxylase or tyrosine 3-monooxygenase is the enzyme responsible for catalyzing the conversion of the amino acid L-tyrosine to L-3,4-dihydroxyphenylalanine (L-DOPA). [ 5 ] [ 6 ] It does so using molecular oxygen (O 2 ), as well as iron (Fe 2+ ) and tetrahydrobiopterin as cofactors .
HPPD is categorized within a class of oxygenase enzymes that usually utilize α-ketoglutarate and diatomic oxygen to oxygenate or oxidize a target molecule. [5] However, HPPD differs from most molecules in this class due to the fact that it does not use α-ketoglutarate, and it only utilizes two substrates while adding both atoms of diatomic oxygen into the product, homogentisate. [6]
Common O-GalNAc core structures; Core 1, Core 2 and poly-N-acetyllactosamine structures. Addition of N-acetylgalactosamine (GalNAc) to a serine or threonine occurs in the Golgi apparatus, after the protein has been folded. [1] [6] The process is performed by enzymes known as GalNAc transferases (GALNTs), of which there are 20 different types. [6]
This mRNA sequence contains codons: 3 nucleotide long segments that code for a specific amino acid. Ribosomes translate the codons to their respective amino acids. [1] In humans, non-essential amino acids are synthesized from intermediates in major metabolic pathways such as the Citric Acid Cycle. [2]
These domains include an amino terminal pleckstrin homology (PH) domain, a proline-rich TEC homology (TH) domain, SRC homology (SH) domains SH2 and SH3, as well as a protein kinase domain with tyrosine phosphorylation activity. [5] Part of the TH domain is folded against the PH domain while the rest is intrinsically disordered.
Tyrosine hydroxylase is the rate limiting enzyme responsible for the transformation of L-Tyrosine to L-3,4-dihydroxyphenylalanine , a catecholamine precursor. Catecholamines, dopamine , epinephrine , and norepinephrine , signal different stressors so the body can activate pathways to return towards homeostasis.
There are two types of inhibitor of PPO, those competitive to oxygen in the copper site of the enzyme and those competitive to phenolics. Tentoxin has also been used in recent research to eliminate the PPO activity from seedlings of higher plants. [19] Tropolone is a grape polyphenol oxidase inhibitor. [20]