Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 appear in the genetic code of life.
Cysteine is a semiessential proteinogenic amino acid with the formula HOOC−CH(−NH2)−CH2−SH. The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile. Cysteine is chiral, but interestingly, both D and L-cysteine are found in nature with D-cysteine having been found in developing brain. Cysteine is named after its discovery in urine, which comes from the urinary bladder or cyst, from kystis "bladder".
Asparagine is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group, an α-carboxylic acid group, and a side chain carboxamide, classifying it as a polar, aliphatic amino acid. It is non-essential in humans, meaning the body can synthesize it. It is encoded by the codons AAU and AAC.
Arginine is the amino acid with the formula (H2N)(HN)CN(H)(CH2)3CH(NH2)CO2H. The molecule features a guanidino group appended to a standard amino acid framework. At physiological pH, the carboxylic acid is deprotonated (−CO2−) and both the amino and guanidino groups are protonated, resulting in a cation. Only the l-arginine (symbol Arg or R) enantiomer is found naturally. Arg residues are common components of proteins. It is encoded by the codons CGU, CGC, CGA, CGG, AGA, and AGG. The guanidine group in arginine is the precursor for the biosynthesis of nitric oxide. Like all amino acids, it is a white, water-soluble solid.
Serine is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group, a carboxyl group, and a side chain consisting of a hydroxymethyl group, classifying it as a polar amino acid. It can be synthesized in the human body under normal physiological circumstances, making it a nonessential amino acid. It is encoded by the codons UCU, UCC, UCA, UCG, AGU and AGC.
In chemistry, a disulfide is a compound containing a R−S−S−R′ functional group or the S2−
2 anion. The linkage is also called an SS-bond or sometimes a disulfide bridge and usually derived from two thiol groups.
Glutathione is an organic compound with the chemical formula HOCOCH(NH2)CH2CH2CONHCH(CH2SH)CONHCH2COOH. It is an antioxidant in plants, animals, fungi, and some bacteria and archaea. Glutathione is capable of preventing damage to important cellular components caused by sources such as reactive oxygen species, free radicals, peroxides, lipid peroxides, and heavy metals. It is a tripeptide with a gamma peptide linkage between the carboxyl group of the glutamate side chain and cysteine. The carboxyl group of the cysteine residue is attached by normal peptide linkage to glycine.
In organic chemistry, a thiol, or thiol derivative, is any organosulfur compound of the form R−SH, where R represents an alkyl or other organic substituent. The −SH functional group itself is referred to as either a thiol group or a sulfhydryl group, or a sulfanyl group. Thiols are the sulfur analogue of alcohols, and the word is a blend of "thio-" with "alcohol".
In molecular biology, post-translational modification (PTM) is the covalent process of changing proteins following protein biosynthesis. PTMs may involve enzymes or occur spontaneously. Proteins are created by ribosomes, which translate mRNA into polypeptide chains, which may then change to form the mature protein product. PTMs are important components in cell signalling, as for example when prohormones are converted to hormones.
Lanthionine is a nonproteinogenic amino acid with the chemical formula (HOOC-CH(NH2)-CH2-S-CH2-CH(NH2)-COOH). It is typically formed by a cysteine residue and a dehydrated serine residue. Despite its name, lanthionine does not contain the element lanthanum.
Cystinosis is a lysosomal storage disease characterized by the abnormal accumulation of cystine, the oxidized dimer of the amino acid cysteine. It is a genetic disorder that follows an autosomal recessive inheritance pattern. It is a rare autosomal recessive disorder resulting from accumulation of free cystine in lysosomes, eventually leading to intracellular crystal formation throughout the body. Cystinosis is the most common cause of Fanconi syndrome in the pediatric age group. Fanconi syndrome occurs when the function of cells in renal tubules is impaired, leading to abnormal amounts of carbohydrates and amino acids in the urine, excessive urination, and low blood levels of potassium and phosphates.
Organosulfur chemistry is the study of the properties and synthesis of organosulfur compounds, which are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compounds known are organosulfur derivatives, e.g., saccharin. Nature is abound with organosulfur compounds—sulfur is vital for life. Of the 20 common amino acids, two are organosulfur compounds, and the antibiotics penicillin and sulfa drugs both contain sulfur. While sulfur-containing antibiotics save many lives, sulfur mustard is a deadly chemical warfare agent. Fossil fuels, coal, petroleum, and natural gas, which are derived from ancient organisms, necessarily contain organosulfur compounds, the removal of which is a major focus of oil refineries.
S-Allylcysteine (SAC) is an organosulfur compound that has the formula HO2CCH(NH2)CH2SCH2C=CH2. It is the S-allylated derivative of the amino acid cysteine. As such only the L-enantiomer is significant biologically. SAC constituent of aged garlic. A number of related compounds are found in garlic, including the disulfide S-"allylmercaptocysteine" and γ-glutamyl-S-allylcysteine" (GSAC).
Cysteine metabolism refers to the biological pathways that consume or create cysteine. The pathways of different amino acids and other metabolites interweave and overlap to creating complex systems.
Sulfur assimilation is the process by which living organisms incorporate sulfur into their biological molecules. In plants, sulfate is absorbed by the roots and then be transported to the chloroplasts by the transipration stream where the sulfur are reduced to sulfide with the help of a series of enzymatic reactions. Furthermore, the reduced sulfur is incorporated into cysteine, an amino acid that is a precursor to many other sulfur-containing compounds. In animals, sulfur assimilation occurs primarily through the diet, as animals cannot produce sulfur-containing compounds directly. Sulfur is incorporated into amino acids such as cysteine and methionine, which are used to build proteins and other important molecules.
O-Acetylserine is an α-amino acid with the chemical formula HO2CCH(NH2)CH2OC(O)CH3. It is an intermediate in the biosynthesis of the common amino acid cysteine in bacteria and plants. O-Acetylserine is biosynthesized by acetylation of the serine by the enzyme serine transacetylase. The enzyme O-acetylserine (thiol)-lyase, using sulfide sources, converts this ester into cysteine, releasing acetate:
Cystine/glutamate transporter is an antiporter that in humans is encoded by the SLC7A11 gene.
Glyceric acid refers to organic compounds with the formula HOCH2CH(OH)CO2H. It occurs naturally and is classified as three-carbon sugar acid. It is chiral. Salts and esters of glyceric acid are known as glycerates.
In biochemistry, non-coded or non-proteinogenic amino acids are distinct from the 22 proteinogenic amino acids, which are naturally encoded in the genome of organisms for the assembly of proteins. However, over 140 non-proteinogenic amino acids occur naturally in proteins and thousands more may occur in nature or be synthesized in the laboratory. Chemically synthesized amino acids can be called unnatural amino acids. Unnatural amino acids can be synthetically prepared from their native analogs via modifications such as amine alkylation, side chain substitution, structural bond extension cyclization, and isosteric replacements within the amino acid backbone. Many non-proteinogenic amino acids are important:
Chloroalanine (3-chloroalanine) is an unnatural amino acid with the formula ClCH2CH(NH2)CO2H. It is a white, water-soluble solid. The compound is usually derived from chlorination of serine. The compound is used in the synthesis of other amino acids by replacement of the chloride. Protected forms of the related iodoalanine are also known.
