Changes

==3. Roles in the Body==

==3. Roles in the Body==

Tyrosine is hydroxylated to 3,4-dihydroxyphenylalanine (DOPA) by tyrosine hydroxylase within different tissues. Depending on where DOPA is produced it can be further converted to dopamine and norepinephrine (e.g., brain and nervous tissue) or melanin (i.e., melanocytes); iodinated tyrosine residues on the thyroglobulin also help form triiodothyronine (T3) and thyroxine (T4) molecules<ref>Stipanuk MH and Watford M. Amino acid metabolism. In Biohemical and physiologic aspects of human nutrition. 2000 Philidelphia, PA: WB Saunders Company p. 270-274.</ref>.

Tyrosine is hydroxylated to 3,4-dihydroxyphenylalanine (DOPA) by tyrosine hydroxylase within different tissues. Depending on where DOPA is produced it can be further converted to dopamine and norepinephrine (e.g., brain and nervous tissue) or melanin (i.e., melanocytes); iodinated tyrosine residues on the thyroglobulin also help form triiodothyronine (T3) and thyroxine (T4) molecules<ref>Stipanuk MH and Watford M. Amino acid metabolism. In Biohemical and physiologic aspects of human nutrition. 2000 Philidelphia, PA: WB Saunders Company p. 270-274.</ref>.

Tyrosine is a precursor to melanin in hair. Twice the amount of phenylalanine and tyrosine are required to produce and maintain a normal black hair coat colour than are required for growth in both dogs and cats<ref name="Bourse">Biourge V and Sergheraert R. Hair pigmentation can be affected by diet in dogs.  Proc Comp Nutr Soc 2002; 4:103-104.</ref><ref name="Yu">Yu SC, et al. Effect of low levels of dietary tyrosine on the hair colour of cats. J Sm Anim Pra 2001;42:176-180.</ref><ref name="Anderson"<Anderson PA, et al. Histidine, phenylalanine-tyrosine and tryptophan requirements for growth of the young kitten. J Anim Sci 1980;50:266-271.</ref>.

Tyrosine is a precursor to melanin in hair. Twice the amount of phenylalanine and tyrosine are required to produce and maintain a normal black hair coat colour than are required for growth in both dogs and cats<ref name="Biourge">Biourge V and Sergheraert R. Hair pigmentation can be affected by diet in dogs.  Proc Comp Nutr Soc 2002; 4:103-104.</ref><ref name="Yu">Yu SC, et al. Effect of low levels of dietary tyrosine on the hair colour of cats. J Sm Anim Pra 2001;42:176-180.</ref><ref name="Anderson">Anderson PA, et al. Histidine, phenylalanine-tyrosine and tryptophan requirements for growth of the young kitten. J Anim Sci 1980;50:266-271.</ref>.

The presence of phenylalanine-containing peptides in the intestinal lumen is a trigger for release of cholecystokinin (CCK)<ref>Koop I and Buchan AM. Cholecystokinin release from isolated canine epithelial cells in short-term culture. Gastroenter 1992;102:28-34.</ref><ref>Backus RC, et al. The potency of dietary amino acids in elevating plasma cholecystokinin immunoreactivity in cats is related to amino acid hydrophobicity. Regul Pept 1997;72:31-40.</ref>.

The presence of phenylalanine-containing peptides in the intestinal lumen is a trigger for release of cholecystokinin (CCK)<ref>Koop I and Buchan AM. Cholecystokinin release from isolated canine epithelial cells in short-term culture. Gastroenter 1992;102:28-34.</ref><ref>Backus RC, et al. The potency of dietary amino acids in elevating plasma cholecystokinin immunoreactivity in cats is related to amino acid hydrophobicity. Regul Pept 1997;72:31-40.</ref>.