One reaction catalyzed by PLP-dependent enzymes is the decarboxylation of amino
ID: 515058 • Letter: O
Question
One reaction catalyzed by PLP-dependent enzymes is the decarboxylation of amino acids. Complete the structure of the "alpha-carbanion" structure which results from the "arrow pash" below by showing any missing lone pairs or formal charges. b. The "alpha-carbanion" structure above is stabilized by delocalization through the PLP to yield what is called the "quinonoid intermediate" shown above. Show "arrow pushes" on your alpha-carbanion structure above which illustrate this delocalization, and which yield structure of the "quinonoid intermediate". The ChemWiki website which we used in class calls PLP an "electron sink" cofactor. What specific feature of PLP allows it to act as an "electron sink"? c. The alpha is then reprotonated (by the H-A shown above it). Show "arrow pushes" for this step on the quinonoid resonance structure which result in "reprotonated alpha carbon" structure shown above. This structure will then yield the decarboxylated amino acid when it undergoes a(n) reaction. d. In the alpha-carbanion resonance structure above the pyridine ring of the PLP is stable because it is ___ but unstable because it is ___. e. In the quiononoid resonance structure the pyridine ring is stable because ___ but unstable because ___.Explanation / Answer
d). In the alpha- carbanion resonance structure of the above pyridine ring of the PLP, the stability is due to high degree of conjugation and delocalisation of the pi electrons. However, unstability arises owing to the positive charge on more elctronegative Nitrogen atom in the structure.
e). In the quiononoid structure, the pyridine ring is stable because of conjugation.
And unstable because of loss of pi electrons possesed by highly electronegative Nitrogen atom.
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