In biochemistry, flavin adenine dinucleotide (FAD) is a redox-active coenzyme associated with various proteins, which is involved with several enzymatic reactions in metabolism. A flavoprotein is a protein that contains a flavin group, which may be in the form of FAD or flavin mononucleotide (FMN). Many flavoproteins are known: components of the succinate dehydrogenase complex, α-ketoglutarate dehydrogenase, and a component of the pyruvate dehydrogenase complex.
Methionine synthase also known as MS, MeSe, MTR is responsible for the regeneration of methionine from homocysteine. In humans it is encoded by the MTR gene (5-methyltetrahydrofolate-homocysteine methyltransferase). Methionine synthase forms part of the S-adenosylmethionine (SAMe) biosynthesis and regeneration cycle, and is the enzyme responsible for linking the cycle to one-carbon metabolism via the folate cycle. There are two primary forms of this enzyme, the Vitamin B12 (cobalamin)-dependent (MetH) and independent (MetE) forms, although minimal core methionine synthases that do not fit cleanly into either category have also been described in some anaerobic bacteria. The two dominant forms of the enzymes appear to be evolutionary independent and rely on considerably different chemical mechanisms. Mammals and other higher eukaryotes express only the cobalamin-dependent form. In contrast, the distribution of the two forms in Archaeplastida (plants and algae) is more complex. Plants exclusively possess the cobalamin-independent form, while algae have either one of the two, depending on species. Many different microorganisms express both the cobalamin-dependent and cobalamin-independent forms.
In enzymology, a hydroxymethylglutaryl-CoA reductase (NADPH) (EC 1.1.1.34) is an enzyme that catalyzes the chemical reaction
In enzymology, a corydaline synthase (EC 2.1.1.147) is an enzyme that catalyzes the chemical reaction
In enzymology, a precorrin-2 C20-methyltransferase is an enzyme that catalyzes the chemical reaction
In enzymology, precorrin-3B C17-methyltransferase is an enzyme that catalyzes the chemical reaction
In enzymology, precorrin-6A synthase (deacetylating) (EC 2.1.1.152) is an enzyme that catalyzes the chemical reaction
In enzymology, a cis-2-enoyl-CoA reductase (NADPH) (EC 1.3.1.37) is an enzyme that catalyzes the chemical reaction
In enzymology, a precorrin-6A reductase (EC 1.3.1.54) is an enzyme that catalyzes the chemical reaction
In enzymology, a cob(II)alamin reductase (EC 1.16.1.4) is an enzyme that catalyzes the chemical reaction
In enzymology, a cyanocobalamin reductase (cyanide-eliminating) (EC 1.16.1.6) is an enzyme that catalyzes the chemical reaction
In enzymology, a CoA-glutathione reductase (EC 1.8.1.10) is an enzyme that catalyzes the chemical reaction
In enzymology, a glutamate synthase (NADPH) (EC 1.4.1.13) is an enzyme that catalyzes the chemical reaction
In enzymology, a NADPH dehydrogenase (quinone) (EC 1.6.5.10) is an enzyme that catalyzes the chemical reaction
Methionine synthase reductase, also known as MSR, is an enzyme that in humans is encoded by the MTRR gene.
Cob(I)yrinic acid a,c-diamide adenosyltransferase, mitochondrial is an enzyme that in humans is encoded by the MMAB gene.
Flavoprotein pyridine nucleotide cytochrome reductases catalyse the interchange of reducing equivalents between one-electron carriers and the two-electron-carrying nicotinamide dinucleotides. The enzymes include ferredoxin-NADP+ reductases, plant and fungal NAD(P)H:nitrate reductases, cytochrome b5 reductases, cytochrome P450 reductases, sulphite reductases, nitric oxide synthases, phthalate dioxygenase reductase, and various other flavoproteins.
In molecular biology, the vitamin B12-binding domain is a protein domain which binds to cobalamin. It can bind two different forms of the cobalamin cofactor, with cobalt bonded either to a methyl group (methylcobalamin) or to 5'-deoxyadenosine (adenosylcobalamin). Cobalamin-binding domains are mainly found in two families of enzymes present in animals and prokaryotes, which perform distinct kinds of reactions at the cobalt-carbon bond. Enzymes that require methylcobalamin carry out methyl transfer reactions. Enzymes that require adenosylcobalamin catalyse reactions in which the first step is the cleavage of adenosylcobalamin to form cob(II)alamin and the 5'-deoxyadenosyl radical, and thus act as radical generators. In both types of enzymes the B12-binding domain uses a histidine to bind the cobalt atom of cobalamin cofactors. This histidine is embedded in a DXHXXG sequence, the most conserved primary sequence motif of the domain. Proteins containing the cobalamin-binding domain include:
In molecular biology, cob(I)yrinic acid a,c-diamide adenosyltransferase EC 2.5.1.17 is an enzyme which catalyses the conversion of cobalamin into one of its coenzyme forms, adenosylcobalamin. Adenosylcobalamin is required as a cofactor for the activity of certain enzymes. AdoCbl contains an adenosyl moiety liganded to the cobalt ion of cobalamin via a covalent Co-C bond.
Cobalamin biosynthesis is the process by which bacteria and archea make cobalamin, vitamin B12. Many steps are involved in converting aminolevulinic acid via uroporphyrinogen III and adenosylcobyric acid to the final forms in which it is used by enzymes in both the producing organisms and other species, including humans who acquire it through their diet.
