Mechanisms of Flavin adenine dinucleotide
The mechanisms below have been extracted from
MACiE. The substrates and products are abstracted to their essential parts,
which are necessary to explain the reaction the cofactor takes part in. The atoms
involved in the next step are highlighted in red, and the ones that have been changed
by the last step are shown in green. Red takes precedence when both applies.
Mechanism #1 for Flavin adenine dinucleotide
Mechanism #2 for Flavin adenine dinucleotide
Mechanism #3 for Flavin adenine dinucleotide
Mechanism #4 for Flavin adenine dinucleotide
Mechanism #5 for Flavin adenine dinucleotide
Mechanism #6 for Flavin adenine dinucleotide
Mechanism #7 for Flavin adenine dinucleotide
Description of mechanism
Flavin cofactors have several different mechanisms, which can be combined in various ways. The mechanism schemes therefore illustrate partial reactions, rather than the overall chemical transformation. [MACiE] Partial mechanisms include:
- Radical mechanism:
After N5 acquires a hydride from a donor, C4a and C10a formally share a double bond. An electron acceptor then takes one of the electrons from that double bonds away whereas the second on formally builds a radical at C4a. This flavin radical can either be used to channel [M0068] or temporarily store electrons[M0130] or to react with another radical [M0103]. Sometimes, the unpaired electron also stays with N10 and abstracts a proton from a donor on arrival of the second single electron [M0139].
- O-mechanism (hydride transfer):
A donor provides a hydride that is attached to N5. This induces concerted double bond rearrangement in which the oxygen atom of the carbonyl group at C2 acts as an electron sink. The free electron pair of this oxygen atom then abstracts a proton from a donor. The reverse reaction takes then place such that the hydride at N5 can be transferred to the substrate [M0003].
- O-mechanism (attachment at C4a):
The flavin again activated by a hydride transfer as described above. The free electron pair at the oxygen attached to C2 returns to C4a and attacks an electrophile (E) which forms a bond to C4a. The former electrophile (E) then abstracts the proton from N5. E can be a reactant [M0110] or an amino acid side chain [M0006]. In the former case, the intermediate form might be a FAD radical and a reactant radical, before attachment occurs.
- N-mechanism:
In this case, the concerted double bond rearrangement stops at N1, not at the oxygen attached to C2 [M0020].
It has recently been found that a flavin-dependant monooxygenase performs a ping-pong-type reaction mechanism with a reductive and an oxidative half-reaction [6].
References
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