Methionine is an essentail amino acid which is required to be ingested through diet because the human enzymes are not capable of its synthesis. Interestingly, methionine, encoded by the starting codon AUG, is the first amino acid for every protein translated in living cells. It could be removed by post-translational modifications. Nonetheless, without methionine, protein translation could not be initiated. Hence, the presence of methionine is absoluately esential for the proper functioning of normal body metabolism and activity. In plants and micro-organisms, methionine is syntehsized from aspartic acid and cysteine.
Methionine is often most proned to being the limiting amino acid in dogs and cats because of its ability to act as a donor or an acceptor of functional groups. In other words, methionine can be easily modified. For this reason, crystalline DL-methionine is often incorporated as a supplement in pets feed. It increases the health of skins and furs, eyes, heart, and more. As a sulfur donor, it can also act as an indicator of vitamin B concentrations. While more expensive than its substitue, HMA, methionine is less corrossive and does not require specialized equipment and plumbing for handling and mixing. In addition, animals need to transfer HMA into the liver for oxidation and transamination modifications, whereas methionine is more biologically available.
Deficiency in methionine can cause apathy, edema, lethargy, muscle and fat loss, liver damage, and reduced growth in children. Methionine is also vital in regulating the flow of folic acid, which is espcially important during pregnancy. Other uses of methionine include treating depression, alcholism, liver disease, allergies and asthma. Furthermore, methionine is known to be very effective in reducing toxic effects from radiation, surgery, and other injuries.
Sources of methionine include sesame seeds, Brazil nuts, fish, meats, and some plant seeds. In most cases, fruits and vegetables do not contain a significant level of methionine with the exception of spinach, potatoes, and cooked corn. Legumes, although high in protein content, contain very little amount of methionine.
References: (1) http://www.mineralsinc.com/WriteUp /ZincAscorbate_w.htm (2) http://en.wikipedia.org/wiki/Zinc (3) http://www.health4youonline.com/health_supplements _biocare_nutrisorb_zinc_b257.htm
