Role As A Coenzyme
PLP acts as a coenzyme in all transamination reactions, and in some decarboxylation and deamination reactions of amino acids. The aldehyde group of PLP forms a Schiff-base linkage (internal aldimine) with the ε-amino group of a specific lysine group of the aminotransferase enzyme. The α-amino group of the amino acid substrate displaces the ε-amino group of the active-site lysine residue. The resulting external aldimine becomes deprotonated to become a quinoid intermediate, which in turn accepts a proton at a different position to become a ketimine. The resulting ketimine is hydrolysed so that the amino group remains on the complex.
In addition, PLP is used by aminotransferases (or transaminases) that act upon unusual sugars such as perosamine and desosamine. In these reactions, the PLP reacts with glutamate, which transfers its alpha-amino group to PLP to make pyridoxamine phosphate (PMP). PMP then transfers its nitrogen to the sugar, making an amino sugar.
PLP is also involved in various beta-elimination reactions such as the reactions carried out by serine dehydratase and GDP-4-keto-6-deoxymannose-3-dehydratase (ColD).
It is also active in the condensation reaction in heme synthesis.
PLP plays a role in the conversion of dopa into dopamine, allows the conversion of the excitatory neurotransmitter glutamate to the inhibitory neurotransmitter GABA, and allows SAM to be decarboxylated to form propylamine, which is a precursor to polyamines.
Read more about this topic: Pyridoxal Phosphate
Famous quotes containing the words role as and/or role:
“American feminists have generally stressed the ways in which men and women should be equal and have therefore tried to put aside differences.... Social feminists [in Europe] ... believe that men and society at large should provide systematic support to women in recognition of their dual role as mothers and workers.”
—Sylvia Ann Hewitt (20th century)
“The trouble is that the expression material thing is functioning already, from the very beginning, simply as a foil for sense-datum; it is not here given, and is never given, any other role to play, and apart from this consideration it would surely never have occurred to anybody to try to represent as some single kind of things the things which the ordinary man says that he perceives.”
—J.L. (John Langshaw)