Sulphur Amino Acids

The sulphur amino acids of particular relevance here are methionine and cysteine. In proteins, 2 mol of cysteine may undergo oxidation to form a disulphide bridge, yielding another sulphur amino acid, cystine. Methionine plays a key role in metabolism as a donor of active methyl groups. It does so after conversion into S-adenosylmethionine. Following release of the active methyl group, S-adenosylhomocysteine is formed which may then undergo hydrolysis to produce homocysteine. The importance of homocysteine in human health has recently been recognized following demonstrations of elevated plasma levels of the amino acid in patients with coronary, cerebrovascular and peripheral arterial occlusive disease. In addition, the role of homocysteine in embryonic development may have implications in animal

Excretion in faeces and/or urine

Mimosine Metabolism The Ruminant



Excretion in faeces and/or urine

Non-toxic residues cc


  1. 4.5. Mimosine metabolism in the ruminant (D'Mello, 1991).
  2. The 'homocysteine as a terato- The biosynthesis of cysteine from gen' hypothesis has been tested partly by methionine relies on the initial formation of employing a chicken embryo model homocysteine which then donates its sul-

(Rosenquist and Finnell, 2001). phur atom to serine to yield cystathionine.

Ribose-5-p hosphate

5-Phosphoribosyl-1-pyrophosphate (PRPP) (g) ^r Glutamine

5-Phosphoribosylamine r— Glycine

Glycinamide ribonucleotide - Glutamine

Formylglycinamidine ribonucleotide


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