odd chain fatty acid

[dontwantaids]

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hey guys this is really buggin me.. plz help

beta oxidation of palmitate (16 carbon--even chain fatty acid) will yield 8 acetyl coa... and we can easily calculate total amount of atp produced in this reaction because each acetyl coa yeilds 12 atp in the tca cycle ...after calculating the atps used, atps gained and atp yeild from acetyl coa, it turns out that palmitate yeilds 129 atp....but beta oxidation of odd chain fatty acid, from what i understand, ultimately yeilds acetyl coa and propionyl coa which is ultimately converted to succinyl coa... how can we calculate number of atps produced in this situation...

or in short, how can we calculate number of atps produced from beta oxidation of an odd chain fatty acid (say 17 carbon long)???

thanx in advance 🙂

 

[avishkar1984]

odd chain fatty acids break down to give acetyl coA + propionyl coA
so, if u hv a 17 carbon fatty acid, it will give
7 acetyl coA + 1 propionyl coA

each acetyl coA yields 12 atps and hence 7 will yield 84 atps
the propionyl coA gets converted into succinyl coA which is an intermediate in the TCA cycle
so it does not yield any atps

 

[dontwantaids]

hey thanks so much avishkar.. i was confsed bcuz i thought succinyl coa would go into tca cycle, convert into succinate, then fumerate, then malate, then oxaloacetate, yielding atps on the way... why doesn't it.. aren't the enzymes available?

 

[nist7]

From my professor and from a quick search in the NIH book database, it seems that the modern and more correct number for ATP generation is not 2 for FADH2 and 3 for NADH, but rather 1.5 ATP for each FADH2 and 2.5 ATP for each NADH.
http://web.indstate.edu/thcme/mwking/oxidative-phosphorylation.html#complexes
http://www.ncbi.nlm.nih.gov/books/b... phosphorylation&rid=stryer.section.2569#2571

Thus, a 16 carbon fatty acid will generate 108 gross ATPs (net is only 106 since "two" ATPs are used in its activation..ATP to AMP + PPi)

Applying this to the NADH and FADH2 generated by Acetyl-CoA in the TCA, you get a net synthesis of 10 ATP for each Acetyl-CoA, not 12.

Succinyl-CoA is an intermediate in the TCA cycle but I am wary to conclude that it will NOT generate any ATPs. (subsequent reactions produce GTP, FADH2, and a NADH as products) Seeing that I am in a biochem course now, I probably should've asked the professor. Albeit he did not go over odd-fatty acid degradation in much detail at all. Not sure if this will be tested on the Step 1, but nevertheless....

 

[avishkar1984]

i think the biochem video lectures clearly mention that all the intermediates are interconverted from one to another only for the transfer utilization of acetyl coA for generation of ATP
so as far as i know the intermediates are meaningless by themselves if no acetyl CoA is present
had it not been this way then we would not need acetyl coA for generation of any ATP
the cycle would go on and on forever(AND WE WOULD NEVER HAVE HAD TO EAT!!!!!....😉)
and as far as the 1.5 and 2.5 ATP thing goes
well i think it has been around for some time now(about 7-8 yrs)
i read it in school as far as i remember
but for all practical purposes we use the figures 2 and 3 for fadh2 and nadh2 respectively
👍

 

[nist7]

The intermediates might not be completely "meaningless" if they are introduced into the cycel "de novo." After all, we are burning up a fatty acid molecule. Although I understand that an acetyl-coa is needed to "start" the TCA, some intermediates might be shunted off to other pathways. The enzymes will work according to their appropriate substrates and other regulatory mechanisms. The Succinyl-CoA dehydrogenase can and will catalyze multiple rounds of redox reactions...thus if you introduce an additional Succinyl-CoA molecule into the cycle (at which point the two carbons from acetyl-coa has already left) the enzyme will do its job and make GTP. Subsequent reactions in the cycle will further generate another FADH2 and NADH.

My point here being that if introduce a NET amounf of the appropriate intermediates is introduced into the TCA cycle, it will be worked on by the enzymes regardless and generate the appropriate products. I'm still awaiting confirmation from my biochem prof.

With regards to NADH and FADH2 and ATP, it seems troubling. Although I doubt the Step 1 will get into THAT kind of minutiae detail.

 

[dontwantaids]

avishkar1984:
"and as far as the 1.5 and 2.5 ATP thing goes well i think it has been around for some time now(about 7-8 yrs) i read it in school as far as i remember
but for all practical purposes we use the figures 2 and 3 for fadh2 and nadh2 respectively"
👍
My prof mentioned that some authors chose to use 1.5 and 2.5 and others 2 and 3.... but the latter seems simpler i guess

nist7... let us know what ur profs say abt the atps yeild..
my prof has "NO idea, sry"

 

[avishkar1984]

my profs stick with the 2 and 3 atps
these seem to be the more popular
but i guess it isnt that high yield for the usmle

 

[dontwantaids]

yea not at all... usmle is more clinically oriented... i guess this is like doing crossword puzzles... jus some mind boggling fun..lol

 

[osli]

IIRC the 1.5/2 and 2.5/3 come from which shuttle system is used to move electrons into the ETC, right? Like asparte-malate vs. glycerol-P shuttles? Max is 2 and 3, but lower yield pathways exist. I'm not sure if one is used preferentially in some circumstances vs. others or if they are both utilized about equally... I'm guessing the former but that seems beyond the scope of review books I've seen. Maybe in a primary biochem text.

 

[excalibre]

odd chain fatty acids break down to give acetyl coA + propionyl coA
so, if u hv a 17 carbon fatty acid, it will give
7 acetyl coA + 1 propionyl coA

each acetyl coA yields 12 atps and hence 7 will yield 84 atps
the propionyl coA gets converted into succinyl coA which is an intermediate in the TCA cycle
so it does not yield any atps

OK, this is gonna be harsh but WRONG!

You're right about the acetyl-CoAs. They each yield 10 or 12 ATPs (whatever the most up-to-date guestimate is).

You are remembering that acetyl-CoAs can never net synthesize glucose, and that is because the carbons essentially turn into CO2 before you get around to oxaloacetate.

BUT, when you add intermediates into the TCA cycle - called an anaplerotic rxn - you essentially 'go around the TCA' until all the carbons are gone, and can create glucose.

For propionyl-CoA you go to succinyl-CoA which uses to ATP equivalents (ATP -> AMP) via these three enzymes propionyl-CoA carboxylase then racemase then methyl-malonyl-CoA mutase.

The succinyl-CoA then goes around Kreb's to oxaloacetate yielding a GTP an FADH2 and then an NADH. Oxaloacetate can then exit Kreb's via PEP carboxykinase using a GTP to yeild a CO2 and a PEP. PEP yields pyruvate, which then does one round of Kreb's.

I haven't done the math, and don't care to. It should be something along the lines of 15 ATPs though.

You could also exit Kreb's via malic enzyme, but I forget how many ATPs that pathway yields.