Methionine is an essential amino acid in humans.
Pyridoxal phosphate (PLP, pyridoxal 5'-phosphate, P5P), the active form of vitamin B6, is a coenzyme in a variety of enzymatic reactions. The International Union of Biochemistry and Molecular Biology has catalogued more than 140 PLP-dependent activities, corresponding to ~4% of all classified activities. The versatility of PLP arises from its ability to covalently bind the substrate, and then to act as an electrophilic catalyst, thereby stabilizing different types of carbanionic reaction intermediates.
In molecular biology, biosynthesis is a multi-step, enzyme-catalyzed process where substrates are converted into more complex products in living organisms. In biosynthesis, simple compounds are modified, converted into other compounds, or joined to form macromolecules. This process often consists of metabolic pathways. Some of these biosynthetic pathways are located within a single cellular organelle, while others involve enzymes that are located within multiple cellular organelles. Examples of these biosynthetic pathways include the production of lipid membrane components and nucleotides. Biosynthesis is usually synonymous with anabolism.
Amino acid synthesis is the set of biochemical processes by which the amino acids are produced. The substrates for these processes are various compounds in the organism's diet or growth media. Not all organisms are able to synthesize all amino acids. For example, humans can synthesize 11 of the 20 standard amino acids. These 11 are called the non-essential amino acids).
Cystathionine-β-synthase, also known as CBS, is an enzyme (EC 4.2.1.22) that in humans is encoded by the CBS gene. It catalyzes the first step of the transsulfuration pathway, from homocysteine to cystathionine:
Serine dehydratase or L-serine ammonia lyase (SDH) is in the β-family of pyridoxal phosphate-dependent (PLP) enzymes. SDH is found widely in nature, but its structure and properties vary among species. SDH is found in yeast, bacteria, and the cytoplasm of mammalian hepatocytes. SDH catalyzes the deamination of L-serine to yield pyruvate, with the release of ammonia.
The enzyme cystathionine γ-lyase (EC 4.4.1.1, CTH or CSE; also cystathionase; systematic name L-cystathionine cysteine-lyase (deaminating; 2-oxobutanoate-forming)) breaks down cystathionine into cysteine, 2-oxobutanoate (α-ketobutyrate), and ammonia:
The transsulfuration pathway is a metabolic pathway involving the interconversion of cysteine and homocysteine through the intermediate cystathionine. Two transsulfurylation pathways are known: the forward and the reverse.
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:
In enzymology, an aspartate racemase is an enzyme that catalyzes the following chemical reaction:
The enzyme cysteine lyase catalyzes the chemical reaction
The enzyme L-3-cyanoalanine synthase catalyzes the chemical reaction
The enzyme threonine synthase (EC 4.2.3.1) catalyzes the chemical reaction
The enzyme phosphoserine phosphatase (EC 3.1.3.3) catalyzes the reaction
In enzymology, a serine O-acetyltransferase is an enzyme that catalyzes the chemical reaction
In enzymology, a cysteine synthase is an enzyme that catalyzes the chemical reaction
In enzymology, an O-acetylhomoserine aminocarboxypropyltransferase is an enzyme that catalyzes the chemical reaction
O-phospho-L-seryl-tRNA:Cys-tRNA synthase is an enzyme with systematic name O-phospho-L-seryl-tRNACys:hydrogen sulfide 2-aminopropanoate transferase. This enzyme catalyses the following chemical reaction
Phosphoserine transaminase is an enzyme with systematic name O-phospho-L-serine:2-oxoglutarate aminotransferase. This enzyme catalyses the following chemical reaction
O-phospho-L-serine—tRNA ligase is an enzyme with systematic name O-phospho-L-serine:tRNACys ligase (AMP-forming). This enzyme catalyses the following chemical reaction:
