[Morgrothiel]

Hi,

I am a bit fresh when it comes to organci chemistry. I am trying to learn a bit about beta-oxidation. On the internet I found this:

http://www.gwu.edu/~mpb/betaox.htm

So, my question is: What does the rounded arrow between FAD and FADH2 mean?

[Borek]

FAD is being reduced to FADH₂ in the reaction. Note that this is only a scheme, not detailed mechanism. However, reaction needs FAD to proceed.

[Morgrothiel]

Ok, so the arrow doesnt really mean anything? Would it mean the same if they wrote

Palmitoyl-CoA (16:0)  +  FAD ==> trans-D2-Palmitenoyl-CoA (16:1tD2) FADH2

?

[Borek]

Something like that. Although it will be better if someone more organically inclined will comment on the subject

[kremar]

wen describing the reactions in a methabolic pathway, the usual notation is to write only 1 reactant and 1 product: the molecule being metabolized, and the molecule it metabolizes into. any other reactives written with an arrow going in the same direction of the reaction, and any other product is written likewise, with an arrow coming out of the reaction.

I think one advantage of that notation over writing "A + B + C => D + E + F" is that this notation makes it look like A, B and C all get toghether, and react in the same spot. The notation with 1 product and 1 reactive clearly distinguishes between the product that binds to the main active site of the enzyme, and the cofactors, which dont necesarily have to act on the same spot.

FAD/FADH2 is a special case, however, since unlike NAD+/NADH or NADP+/NADPH, FAD/FADH2 is a covalently-bound cofactor of the enzyme involved. Writing "A + FAD => B + FADH2" would make it see as if FAD/FADH2 were molecules that could move around freely before and after the reaction, which is not the case: its the Acyl-CoA-deshydrogenase enzyme which acts as an electron carrier. There's another active site of that enzime which binds to ETF (electron transferring flavoprotein), regenerating its FAD cofactor. ETF then binds to another enzyme called ETF:Q oxidoreductase, which passes on the electrons from the reduced ETF to coenzyme Q, regenerating the oxidized ETF and yielding QH2, which can now go on to the oxidative phosphorylation system...