The Sulfur-Containing Amino Acids: An Overview

Abstract

Methionine, cysteine, homocysteine, and taurine are the 4 common sulfur-containing amino acids, but only the first 2 are incorporated into proteins. Sulfur belongs to the same group in the periodic table as oxygen but is much less electronegative. This difference accounts for some of the distinctive properties of the sulfur-containing amino acids. Methionine is the initiating amino acid in the synthesis of virtually all eukaryotic proteins; N-formylmethionine serves the same function in prokaryotes. Within proteins, many of the methionine residues are buried in the hydrophobic core, but some, which are exposed, are susceptible to oxidative damage. Cysteine, by virtue of its ability to form disulfide bonds, plays a crucial role in protein structure and in protein-folding pathways. Methionine metabolism begins with its activation to S-adenosylmethionine. This is a cofactor of extraordinary versatility, playing roles in methyl group transfer, 5'-deoxyadenosyl group transfer, polyamine synthesis, ethylene synthesis in plants, and many others. In animals, the great bulk of S-adenosylmethionine is used in methylation reactions. S-Adenosylhomocysteine, which is a product of these methyltransferases, gives rise to homocysteine. Homocysteine may be remethylated to methionine or converted to cysteine by the transsulfuration pathway. Methionine may also be metabolized by a transamination pathway. This pathway, which is significant only at high methionine concentrations, produces a number of toxic endproducts. Cysteine may be converted to such important products as glutathione and taurine. Taurine is present in many tissues at higher concentrations than any of the other amino acids. It is an essential nutrient for cats.

Importance of Methionine Metabolism in Morula-to-blastocyst Transition in Bovine Preimplantation Embryos

“…Thus, we cannot exclude the possibility that methionine, through the conversion to SAM, regulates Na/K-ATPase-mediated blastocoelic cavitation, as suggested by Bonilla et al [9]. Furthermore, the impaired blastocyst development induced by ethionine was not completely recovered by SAM, suggesting that SAM-independent roles of methionine such as a source of protein synthesis are also important in bovine blastocyst development [1,2]. Importantly, the results of the present study indicate that disruption of methionine metabolism is critical for development after zygotic gene activation (ZGA), which is considered to occur at the 8-cell stage in the case of bovine [39,40].…”

“…Dev. 58: [91][92][93][94][95][96][97] 2012) M ethionine is a dietary essential amino acid that plays multiple biological roles, including those as the initiating amino acid in eukaryotic protein synthesis, a precursor of the essential methyl donor for methylation reactions (S-adenosylmethionine, SAM) and a source of redox regulators (cysteine and glutathione) [1,2]. Methionine metabolism can be seen as the trans-and remethylation cycle of methionine (methionine cycle) that intertwines with the cycle of folate metabolism (folate cycle) and the transsulfuration pathway from homocysteine, an intermediate in the methionine cycle [3], and these combined metabolic networks are called one-carbon metabolism [4,5].…”

Methionine transmethylation and transsulfuration in the piglet gastrointestinal tract

“…Methionine is an indispensable amino acid and is transmethylated intracellularly to homocysteine via S-adenosylmethionine (SAM), an important methyl donor for most biological methylation reactions (1). Homocysteine can be further catabolized to cysteine through transsulfuration, which is regulated by the enzymes cystathionine ␤-synthase (CBS) (EC 4.2.1.22) and cystathionine ␥-lyase (EC 4.4.1.1).…”

Evaluation of various sulphur amino acid to lysine ratio for growing-finishing pigs fed antibiotic-free diets

“…It is suggested that about 30% of the dietary SAA is utilised by the gut for epithelial cell differential and mucosal growth (BauchartThevret et al 2009). Furthermore, available literature indicated that SAA could stimulate humoral and cellmediated immune responses and the metabolites from Met possess pro-and anti-inflammatory properties (Hunter & Grimble 1994;Brosnan & Brosnan 2006). The feeding programmes without in-feed antibiotic may alter the SAA requirement for optimal performance.…”