Changes

==Why are they Important?==

==Why are they Important?==

Both methionine and cysteine are incorporated into structural protein and are '''required for normal growth'''. The sulphur side chains help stabilize secondary and tertiary protein structures. Methionine is part of the [[Nutrition Glossary#Coenzyme|coenzyme]] S-adenosyl methionine, which influences and regulates the activity of a number of enzymatic and cellular replication processes.

Both methionine and cysteine are incorporated into structural [[Protein Overview - Nutrition|protein]] and are '''required for normal growth'''. The sulphur side chains help stabilize secondary and tertiary protein structures. Methionine is part of the [[Nutrition Glossary#Coenzyme|coenzyme]] S-adenosyl methionine, which influences and regulates the activity of a number of enzymatic and cellular replication processes.

Inherited defects in the transporter for dibasic amino acids can result in poor absorption of cyst(e)ine (as well as the other dibasic amino acids [[Lysine - Nutrition|lysine]], ornithine, and [[Arginine - Nutrition|arginine]]) from the intestinal mucosa and poor reabsorption in the renal tubule<ref name="Hoppe">Hoppe A, et al. Urinary excretion of amino acids in normal and cystinuric dogs. Br Vet J 1993;149:253-68.</ref>. Unlike lysine, ornithine and arginine, cystine is not soluble in urine and readily forms [[Urolithiasis|crystals and stones]]. Cystinuria and related dysuria and urinary obstructions due to cystine urolithiasis have been described in Newfoundlands, English bulldogs, and Dachshunds<ref name="Brons">Brons AK, et al. SLC3A1 and SLC7A9 mutations in autosomal recessive or dominant canine cystinuria: A new classification system. JVIM 2013;27:1400-1408.</ref>. Increased intake of DL-methionine (either in the diet or as a supplement) has been used as a therapeutic treatment for sterile struvite crystalluria and urolithiasis<ref name="Lemann">Lemann J and Relman AS. The relation of sulfur metabolism to acid-base balance and electrolyte excretion: the effects of DL-methionine in normal man. J Clin Invest 1959;38:2215-2223.</ref><ref name="Mishina">Mishina M et al. Medical dissolution of struvite nephrolithiasis using amino acid preparations in dogs. JVIM 2000;62:889-892.</ref>. The oxidation of dietary sulphur increases urinary excretion of ammonium (NH₄⁺) resulting in a more acidic urinary pH.

Inherited defects in the transporter for dibasic amino acids can result in poor absorption of cyst(e)ine (as well as the other dibasic amino acids [[Lysine - Nutrition|lysine]], ornithine, and [[Arginine - Nutrition|arginine]]) from the intestinal mucosa and poor reabsorption in the renal tubule<ref name="Hoppe">Hoppe A, et al. Urinary excretion of amino acids in normal and cystinuric dogs. Br Vet J 1993;149:253-68.</ref>. Unlike lysine, ornithine and arginine, cystine is not soluble in urine and readily forms [[Urolithiasis|crystals and stones]]. Cystinuria and related dysuria and urinary obstructions due to cystine urolithiasis have been described in Newfoundlands, English bulldogs, and Dachshunds<ref name="Brons">Brons AK, et al. SLC3A1 and SLC7A9 mutations in autosomal recessive or dominant canine cystinuria: A new classification system. JVIM 2013;27:1400-1408.</ref>. Increased intake of DL-methionine (either in the diet or as a supplement) has been used as a therapeutic treatment for sterile struvite crystalluria and urolithiasis<ref name="Lemann">Lemann J and Relman AS. The relation of sulfur metabolism to acid-base balance and electrolyte excretion: the effects of DL-methionine in normal man. J Clin Invest 1959;38:2215-2223.</ref><ref name="Mishina">Mishina M et al. Medical dissolution of struvite nephrolithiasis using amino acid preparations in dogs. JVIM 2000;62:889-892.</ref>. The oxidation of dietary sulphur increases urinary excretion of ammonium (NH₄⁺) resulting in a more acidic urinary pH.