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As I understand it, lipoic acid is synthesized from octanoic acid:

Lipoic acid is synthesized de novo in mitochondria from octanoic acid, an 8-carbon fatty acid (C8:0), bound to the acyl-carrier protein (ACP; see article on Pantothenic Acid) during the process of fatty acid synthesis (Figure 2).

However, I am wondering how much is actually contained within octanoic acid? Such as if you had 100 ml of octanoic acid, how much lipoic acid would you consume?

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    $\begingroup$ Whatever the acid chosen, it cannot "contain" another acid. It does not contain any other substance $\endgroup$
    – Maurice
    Commented Jan 18, 2021 at 15:29
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    $\begingroup$ I would be very surprised if you ever found any detectable amount of lipoic acid in any prep of octanoic acid, even if it were purified from a biological source. Lipoic acid concentrations are never high in the cell relative to other fatty acids, and any procedure for isolating octanoic from other acids would easily remove it. The typical challenge is removing other acids with slightly longer or short chains which may be fairly abundant depending on the source oil. $\endgroup$
    – Andrew
    Commented Jan 18, 2021 at 16:57
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    $\begingroup$ The phrasing is a bit confusing, perhaps. When you ask how much lipoic acid you would "consume", did you mean "produce"? Also, chemical reactions are... kind of like recipes, but they aren't recipes: firstly as z1273 rightly mentioned one would typically measure in terms of moles, not 100 ml, and secondly we don't really talk about a reactant being "contained within" a product like how a cake contains 150 g of chocolate, because when the reaction is done, the reactants cease to exist — they aren't a thing anymore. This is what Maurice's comment means, and why there's some confusion in ... $\endgroup$
    – orthocresol
    Commented Jan 19, 2021 at 1:09
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    $\begingroup$ ... in the answers about what you're actually asking about. The two answerers have quite different interpretations of your question. Andrew is answering the more literal question of "how much lipoic acid can you find in an extract of octanoic acid", and z1273 the implied question of "how much lipoic acid is used to make one molecule of octanoic acid". Which is your question? I don't mind helping to edit your question, but I can't really tell. Ping me if you need any help. $\endgroup$
    – orthocresol
    Commented Jan 19, 2021 at 1:12
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    $\begingroup$ Ah, ok. Yeah, that's not what "derived" means. Here, "derived" doesn't mean "physically extracted" like how one might extract a component of crude oil; it's more like "synthesised", as in a machine (well, a series of proteins) which you feed octanoic acid to, it does a bunch of things with it, and spits out lipoic acid. So indeed, as you say, there is no lipoic acid "available" before these proteins work their magic on octanoic acid. $\endgroup$
    – orthocresol
    Commented Jan 19, 2021 at 16:03

2 Answers 2

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Background
One lipoic acid molecule is enzymatically produced from one octanoic acid molecule in the mitochondrion or in the bacterium by the enzyme lipoyl synthase (LipA).

Molecules

To get there, first the octanoic acid must be covalently linked to the small protein acyl carrier protein (ACP). This attachment is made at its carboxylic acid end (right end of the molecule shown above).

Then, the octanoate-AcylCarrierProtein binds to the LipA enzyme. LipA contains a [4Fe-4S] center that reacts with the lipidic end of the octanoic acid (left end of the molecule above). The iron-sulfur cluster is highly reactive. At the outset of the reaction, the enzyme leaves one sulfur atom of its iron-sulfur cluster to the third carbon atom from the left and another sulfur atom to the terminal CH3. The resulting product is released from LipA.

Separately the ACP is removed and the two sulhydryl groups chemically oxidize together to a disulfide bond, thus producing the Lipoic acid molecule as illustrated above.

I recommend examining the Scheme 2 in McLaughlin et al., 2016 for details of the catalytic mechanism in a bacterium, Mycobacterium tuberculosis leading to the Lipoic acid product, in the acyl carrier protein bound form.

OP questions

a) The whole of the Octanoic acid, except for two hydrogen atoms are included in the resulting lipoic acid. So it is one to one in molar ratio.

b) I think it may be easier to refer to molar equivalents instead of volume equivalents.

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    $\begingroup$ OPs question is how much lipoic acid is contained in octanoic acid, not how many atoms of octanoic acid are incorporated into lipoic acid. $\endgroup$
    – Andrew
    Commented Jan 18, 2021 at 23:09
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    $\begingroup$ @Andrew I think the OP further specified their question with 'Can you please explain then how is it [lipoic acid] derived from octanoic acid?" Hopefully the details I provided help along those lines, particularly as I tried to place it in the context of the original post. Just trying to help.. $\endgroup$
    – z1273
    Commented Jan 18, 2021 at 23:29
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Fatty acids that are purified from biological sources are typical isolated from oils or fats, both of which are comprised of triglycerides. That is, there are three fatty acids attached to a single glycerol molecule via ester linkages.

Different oils and fats contain different amounts of each fatty acid. For example, a good source of octanoic acid is coconut oil, of which about 8% of the fatty acids are octanoic acid.

Production of pure octanoic acid requires hydrolyzing the oil and using various refining techniques to separate the fatty acids by length.

Triglycerides are formed at the end of the biosynthesis of the individual fatty acids. Although lipoic acid is derived from octanoic acid, the octanoic acid used for this purpose is diverted into the lipoic acid pathway before incorporation into triglycerides. Thus, the triglycerides used for octanoic acid isolation are very unlikely to contain any lipoic acid.

Instead the biosynthesized lipoic acid is contained in the cell attached to various proteins that use it as a reactant in the reactions they catalyze.

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