Q29-14P
Question
Write a mechanism for step 6 of gluconeogenesis, the reduction of 3-phoshoglyceryl phosphate with NADH/H+ to yield glyceraldehyde 3-phosphate.
Step-by-Step Solution
VerifiedA Double Bond rearrangement to an isomeric imine and hydrolysis follows the initial imine synthesis between PMP and a-ketoglutarate.
The Metabolic process of deamination that causes protein catabolism is referred to as transamination. Protein degradation is catabolism.
Protein breakdown (degradation) or catabolism is substantially more complicated than lipids and carbohydrates since each of the 20 α-amino acids has its own unique mechanism of degradation.
The process of deamination is carried out using the -NH2 reacts with the -NH2 in a transamination process. The amino acid's (amino) group is exchanged with the keto group of α-ketoglutarate, resulting in the formation of a new α-keto acid plus glutarate.
The whole process is divided into two phases, each of which is catalyzed by aminotransferases and involves the enzyme pyridoxal phosphate (PLP), a pyridoxine derivative (vitamin B6). The aminotransferases differ in a number of ways.
Their specificity for amino acids has changed, but the mechanism has not.
The reaction mechanism flowchart is provided, as well as a step-by-step description.
The interaction between the a-amino acid and pyridoxal phosphate begins with an imine connection between the side-chain -NH2 group of a lysine residue in the enzyme and the PLP aldehyde group, which is covalently bound to the aminotransferases.
The automerization of the tautomerized imine is affected by deprotonation of the PLP amino acid imine, resulting in an α-keto acid plus pyridoxamine phosphate PMP.A flow chart depicting the enzyme-catalyzed PLP-dependent transamination of an α-amino acid to an α-keto acid.
An amino acid reacts with a PLP imine bound to the enzyme by adding its -NH2 group to the imine’s C=N link, forming a PLP-amino acid imine and releasing the enzyme amino group.
Deprotonation of the amino acid after adding a carbon, resulting in an intermediate α-keto acid imine.
On the PLP carbon, the α-keto acid imine is reprotanated. Tautomerization of the imine C=N bond is the end outcome of this deprotonation and reprolonation sequence.
By nucleophile addition of water to the C=N link, the α-keto acid imine is hydrolyzed, yielding the transamination products pyridox amine phosphate PMP and α-keto acid.
The interaction of the PLP enzyme-imine with an α-amino acid to give a PLP-amino acid imine plus ejected enzyme as the leaving group is the first step in transamination.
The amino acid -NH2 group is nucleophile added to the C=N bond of the PLP imine, much like an amine is nucleophilely added to the C=0 bond of a ketone in an aldehyde in a nucleophile addition reaction.
To complete the reaction, the protonated di-amine intermediate undergoes a proton transfer and expels the lysine amino group from the enzyme.
Hydrolysis and tautomerization step 2, the C-N bond is tautomerized after the synthesis of the PLP-amino acid imine in step 1.
The protonated pyridine ring of PLP acts as the electron acceptor, while the basic lysine residue in the enzyme that was expelled as a leaving group during transamination deprotonates the addition a-position of the amino acid.
The carbon atom reprotonates, followed by the ring, resulting in a tautomeric product that is the imine of an α-keto acid with PMP.The first phase of the transamination reaction is completed by hydrolysis of this PMP α-keto acid imine.
The mechanistic reversal of imine production happens when water is added as a nucleophile to the imine, followed by proton transfer and PMP ejection as the leaving group.
PLP regeneration from PMP PMP must be transformed now that PLP plus the a-AA has been turned to PMP plus ana-keto acid.
To finish the cetalytie cycle, return to PLP. Another transamination event between PMP and a ketoglutarate results in this conversion.PLP plus glutamate are the end products, and the pathway is depicted here.
PMP and a-ketoglutarate form an imine in this reaction, which then undergoes tautomerization of the C=N bond to form a PLP glutamate imine.
In a transamination reaction, the latter combines with a lysine residue on the enzyme to produce PLP-enzyme imine plus glutamate.
Deamination is the reaction that indicates the mechanistic implication of protein catabolism.