Changes

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.

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 [[Essential Ion and Compound Balance and Homeostasis - Anatomy & Physiology|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.

==Roles in the Body==

==Roles in the Body==

Methionine is part of the coenzyme s-adenosylmethionine, which through its ability to transfer to and methylate other substrates, is able to modify the activities of a range of different metabolic processes including nucleic acids, proteins, lipds and secondary metabolites); it is also a constituent of protein, and a precursor of cysteine<ref name="Stipanuk">Stipanuk MH and Watford M. Amino acid metabolism. In Biochemical and physiologic aspects of human nutrition. 2000 Philidelphia, PA: WB Saunders Company p. 265-270.</ref>.  

Methionine is part of the coenzyme s-adenosylmethionine, which through its ability to transfer to and methylate other substrates, is able to modify the activities of a range of different metabolic processes including nucleic acids, proteins, lipds and secondary metabolites); it is also a constituent of protein, and a precursor of cysteine<ref name="Stipanuk">Stipanuk MH and Watford M. Amino acid metabolism. In Biochemical and physiologic aspects of human nutrition. 2000 Philidelphia, PA: WB Saunders Company p. 265-270.</ref>.  

Cysteine readily forms sulphide bonds with other thiol groups stabilizing secondary and tertiary structure in proteins such as hair, glutathione, and [[insulin]]; and acts as a sulphur donor to [[Vitamin B4 (Choline) - Nutrition|choline]], an essential vitamin-like nutrient<ref name="NRC">National Research Council (NRC). Protein and Amino Acids. In Nutrient Requirements for Dogs and Cats. 2006 Washington, DC: National Academies Press p. 125-126.</ref>. Cysteine is a precursor to [[Taurine - Nutrition|taurine]] in dogs, however cats have low activity of hepatic cysteine dioxygenase and cysteine sulphinate decarboxylase activity (two key enzymes in the conversion of cysteine to taurine) and require a preformed source of taurine in the diet<ref name="De la Rosa">De la Rosa J, et al. Metabolism of cysteine and cyteinesulfinate in rat and cat hepatocytes. J Nutr 1987;117:549-558.</ref>. Cysteine is also a precursor of felinine, a urine pheromone produced by cats that gives cat urine its distinctive aroma<ref name="Hendriks">Hendriks WH, et al. Importance of sulfate, cysteine and methionine as precursors to felinine synthesis by domestic cats (Felis catus). Comp Biochem Physiol C Toxicol Pharmacol 2001;129:211–216.</ref>.

Cysteine readily forms sulphide bonds with other thiol groups stabilizing secondary and tertiary structure in proteins such as [[Hair - Anatomy & Physiology|hair]], glutathione, and [[insulin]]; and acts as a sulphur donor to [[Vitamin B4 (Choline) - Nutrition|choline]], an essential vitamin-like nutrient<ref name="NRC">National Research Council (NRC). Protein and Amino Acids. In Nutrient Requirements for Dogs and Cats. 2006 Washington, DC: National Academies Press p. 125-126.</ref>. Cysteine is a precursor to [[Taurine - Nutrition|taurine]] in dogs, however cats have low activity of hepatic cysteine dioxygenase and cysteine sulphinate decarboxylase activity (two key enzymes in the conversion of cysteine to taurine) and require a preformed source of taurine in the diet<ref name="De la Rosa">De la Rosa J, et al. Metabolism of cysteine and cyteinesulfinate in rat and cat hepatocytes. J Nutr 1987;117:549-558.</ref>. Cysteine is also a precursor of felinine, a urine pheromone produced by cats that gives cat urine its distinctive aroma<ref name="Hendriks">Hendriks WH, et al. Importance of sulfate, cysteine and methionine as precursors to felinine synthesis by domestic cats (Felis catus). Comp Biochem Physiol C Toxicol Pharmacol 2001;129:211–216.</ref>.

==Consequences of Methionine and Cysteine Deficiency==

==Consequences of Methionine and Cysteine Deficiency==

====Dogs:====

====Dogs:====

Puppies fed a methionine deficient diet experience decreased food intake, weight loss and evidence of dermatitis<ref name="Milner">Milner JA. Assessment of indispensable and dispensable amino acids for the immature dog. J Nutr 1979;109:1161-1167.</ref>. In puppies Methionine deficiency in combination with excess cysteine resulted in hyperkaratotic, necrotic foot pad lesions<ref name="Burns">Burns RA and Milner JA. Sulfur amino acid requirements of immature beagle dogs. J Nutr 1982;112:447-452.</ref>, that resolved with reintroduction of methionine. Inadequate intake of sulphur amino acids without supplemental taurine has also been associated with development of taurine deficient cardiomyopathy<ref name="Torres">Torres CL, et al. Taurine status in normal dogs fed a commercial diet associated with taurine deficiency and [[Dilated Cardiomyopathy|dilated cardiomyopathy]]. JAPAN(Berl) 2003;87:359-72.</ref><ref name="Backus">Backus RC, et al. Low Plasma Taurine Concentration in Newfoundland Dogs is Associated with Low Plasma Methionine and Cyst(e)ine Concentrations and Low Taurine Synthesis. J Nutr 2006;136:2525-2533.</ref>, and pigmented gallstones<ref name="Christian">Christian JS and Rege RV. Methionine, but not taurine, protects against formation of canine pigmented gallstones. J Surg Res 1996;61:275-281.</ref> in adult dogs.  

Puppies fed a methionine deficient diet experience decreased food intake, weight loss and evidence of dermatitis<ref name="Milner">Milner JA. Assessment of indispensable and dispensable amino acids for the immature dog. J Nutr 1979;109:1161-1167.</ref>. In puppies, methionine deficiency in combination with excess cysteine resulted in hyperkaratotic, necrotic foot pad lesions<ref name="Burns">Burns RA and Milner JA. Sulfur amino acid requirements of immature beagle dogs. J Nutr 1982;112:447-452.</ref>, that resolved with reintroduction of methionine. Inadequate intake of sulphur amino acids without supplemental taurine has also been associated with development of taurine deficient cardiomyopathy<ref name="Torres">Torres CL, et al. Taurine status in normal dogs fed a commercial diet associated with taurine deficiency and [[Dilated Cardiomyopathy|dilated cardiomyopathy]]. JAPAN(Berl) 2003;87:359-72.</ref><ref name="Backus">Backus RC, et al. Low Plasma Taurine Concentration in Newfoundland Dogs is Associated with Low Plasma Methionine and Cyst(e)ine Concentrations and Low Taurine Synthesis. J Nutr 2006;136:2525-2533.</ref>, and pigmented gallstones<ref name="Christian">Christian JS and Rege RV. Methionine, but not taurine, protects against formation of canine pigmented gallstones. J Surg Res 1996;61:275-281.</ref> in adult dogs.  

====Cats:====  

====Cats:====  

Feeding of a methionine deficient diet to kittens resulted in weight loss, lethargy and abnormal ocular secretions<ref>Teeter RG, et al. Essentiality of methionine in the cat. J Anim Sci 1978;46:1287-1292.</ref><ref>Rogers QR and Morris JG. Essentiality of amino acids for the growing kitten. J Nutr 1979;109:718-723. </ref>. Deficient methionine intake with adequate cysteine supplementation intake in kittens also resulted in severe perioral and foot pad lesions<ref name="NRC"/>.  

Feeding of a methionine deficient diet to kittens resulted in weight loss, lethargy and abnormal ocular secretions<ref>Teeter RG, et al. Essentiality of methionine in the cat. J Anim Sci 1978;46:1287-1292.</ref><ref>Rogers QR and Morris JG. Essentiality of amino acids for the growing kitten. J Nutr 1979;109:718-723. </ref>. Deficient methionine intake with adequate cysteine supplementation intake in kittens also resulted in severe perioral and foot pad lesions<ref name="NRC"/>.

==Toxicity==

==Toxicity==

==Dietary Sources==

==Dietary Sources==

Methionine and cysteine are found in highest concentrations in '''animal proteins''' (e.g., muscle, organ meats, and eggs), and are present but at much lower levels in dairy (e.g., casein), cereal grains, and pulses (i.e., legumes). Methionine and cysteine are often the most limiting amino acid in natural protein sources and are frequently supplemented into commercially-prepared dog and cat foods. Diets containing poorly digestible proteins may be inadequate to supply methionine and cysteine despite having adequate total crude protein levels<ref name="Torres"/>.

Methionine and cysteine are found in highest concentrations in '''animal proteins''' (e.g. muscle, organ meats, and eggs), and are present but at much lower levels in dairy (e.g. casein), cereal grains, and pulses (i.e. legumes). Methionine and cysteine are often the most limiting amino acid in natural protein sources and are frequently supplemented into commercially-prepared dog and cat foods. Diets containing poorly digestible proteins may be inadequate to supply methionine and cysteine despite having adequate total crude protein levels<ref name="Torres"/>.

==Diagnosing Methionine and Cysteine Deficiency==

==Diagnosing Methionine and Cysteine Deficiency==

==References==

==References==

<references/>

<references/>

[[Category:Amino Acids]]

[[Category:Amino Acids]]