Threonine dehydratase () (TDH) catalyzes the dehydratation of threonine into alpha-ketobutarate and ammonia. In Escherichia coli and other microorganisms, two classes of TDH are known to exist. One is involvedin the biosynthesis of isoleucine, the other in hydroxamino acid catabolism.A form of TDH with two copies of the C-terminal domain is described by . This entry describes a phylogenetically distinct form, which includes the catabolic threonine dehydratase of E. coli; many members are designated as catabolic for this reason. The catabolic form appears to lack a domain. Many members of this family are found in species with other isoleucine biosynthetic enzymes.
Threonine dehydratase () (TDH) catalyzes the dehydratation of threonine into alpha-ketobutarate and ammonia. In Escherichia coli and other microorganisms, two classes of TDH are known to exist. One is involvedin the biosynthesis of isoleucine, the other in hydroxamino acid catabolism.This entry describes a form of TDH that is distinct from the clades described by and . The sequences described by this entry have one copy of the threonine dehydratase C-terminal domain (). They are exclusively found in species containing the rest of the isoleucine biosynthesis pathway and which are generally lacking in members of the other two clades of threonine dehydratases. They include mitochondrial and plastid threonine dehydratases.
Thermostable direct haemolysin (TDH) is considered an important virulence factor in Vibrio parahaemolyticus gastroenteritis and is a dimer composed of two identical subunit molecules of approximately 21kDa. The tetrameric form contains a central pore permitting entry and exit of water molecules. A number of biological properties have been attributed to TDH including haemolytic activity, enterotoxicity, cytotoxicity and cardiotoxicity [].
Thermostable direct haemolysin (TDH) is considered an important virulence factor in Vibrio parahaemolyticus gastroenteritis and is a dimer composed of two identical subunit molecules of approximately 21kDa. The tetrameric form contains a central pore permitting entry and exit of water molecules. A number of biological properties have been attributed to TDH including haemolytic activity, enterotoxicity, cytotoxicity and cardiotoxicity [].Structurally, this superfamily consists of 10 beta strands, 1 alpha helix and 1 3(10)-helix.
Threonine dehydratase () (TDH) catalyzes the dehydratation of threonine into alpha-ketobutarate and ammonia. In Escherichia coli and other microorganisms, two classes of TDH are known to exist. One is involvedin the biosynthesis of isoleucine, the other in hydroxamino acid catabolism.This entry describes a form of threonine dehydratase with two copies of the threonine dehydratase C-terminal domain (_. Members with known function participate in isoleucine biosynthesis and are inhibited by isoleucine.
Pyridoxal phosphate is the active form of vitamin B6 (pyridoxine or pyridoxal). Pyridoxal 5'-phosphate (PLP) is a versatile catalyst, acting as a coenzyme in a multitude of reactions, including decarboxylation, deamination and transamination [, , ]. PLP-dependent enzymes are primarily involved in the biosynthesis of amino acids and amino acid-derived metabolites, but they are also found in the biosynthetic pathways of amino sugars and in the synthesis or catabolism of neurotransmitters; pyridoxal phosphate can also inhibit DNA polymerases and several steroid receptors []. Inadequate levels of pyridoxal phosphate in the brain can cause neurological dysfunction, particularly epilepsy [].PLP enzymes exist in their resting state as a Schiff base, the aldehyde group of PLP forming a linkage with the ε-amino group of an active site lysine residue on the enzyme. The α-amino group of the substrate displaces the lysine ε-amino group, in the process forming a new aldimine with the substrate. This aldimine is the common central intermediate for all PLP-catalysed reactions, enzymatic and non-enzymatic [].Serine and threonine dehydratases [, ]are functionally and structurally related pyridoxal-phosphate dependent enzymes. L-serine dehydratase () and D-serine dehydratase () catalyse the dehydratation of L-serine (respectively D-serine) into ammonia and pyruvate. Threonine dehydratase () (TDH) catalyses the dehydratation of threonine into alpha-ketobutarate and ammonia. In Escherichia coli and other microorganisms, two classes of TDH are known to exist. One is involved in the biosynthesis of isoleucine, the other in hydroxamino acid catabolism. Threonine synthase () is also a pyridoxal-phosphate enzyme, it catalyses the transformation of homoserine-phosphate into threonine. It has been shown []that threonine synthase is distantly related to the serine/threonine dehydratases. In all these enzymes, the pyridoxal-phosphate group is attached to a lysine residue.
