Tyrosine is a conditionally essential amino acid that can be ingested through diet or is synthesized in the body from the essential amino acid phenylalanine. Tyrosine is involved in the synthesis of many important compounds, such as pigment melanin, some phenolic compounds, thyroid hormone thyroxine, coenzyme Q10 and is also a precursor of dopamine, noradrenaline and adrenaline, and could therefore act as an agent for mood improvement. Disorders in the metabolism of tyrosine are often the consequence of inborn errors in the metabolism of tyrosine and lack of functional enzymes. There are three types of tyrosinemia, and a few more rare disorders such as Alkaptonuria and Hawkinsinuria. Certain microbial enzymes, often of lactic acid bacteria, catalyze decarboxylation of tyrosine in foods or in gastrointestinal tract into biogenic amine tyramine. Content of tyramine in food depends on factors such as type of food, temperature, pH, salt concentration, and storage conditions. If we ingest too much of this biogenic amine, it can have a negative impact on our health and increase the blood pressure. Tyrosine was also the subject of various studies where its effect on cognitive abilities was examined, however the conclusions of the studies were not uniform regarding the effect of the substance on central nervous system.
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