Methionine

Methionine is an essential, sulphur-containing amino acid with several overlapping jobs. It is a key methyl-group donor in the body's methylation reactions, and it is the precursor of both [cysteine](/glossary/cysteine) and [taurine](/glossary/taurine), so it indirectly helps meet the taurine needs that matter so much in cats. In a meat-based feline diet, methionine is often the most limiting amino acid, which makes it a closely watched formulation parameter. It has a second, practical property: it acidifies the urine, and this is exploited in some urinary-health foods to lower urinary pH and discourage struvite stones, which form preferentially in alkaline urine. Deficiency can impair growth, dull the coat and compromise taurine status, while a marked excess can over-acidify the urine and cause problems of its own, so dosing has to be measured rather than maximised. The richest sources are animal proteins such as meat, fish and egg. On a label you may see synthetic DL-methionine listed among the additives, included either to balance the amino-acid profile or for its urine-acidifying effect. Methionine therefore sits at the crossroads of protein quality, antioxidant supply and urinary health, linking the [essential amino acids](/glossary/essential-amino-acids) to several other entries. See the [Petipedia glossary](/glossary).

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