Glycolysis, Step 6

[samoyan]

Hello,

I have a question regarding Step 6 in glycolysis.
It`s clear that in step 5, two molecules of G3P (glyceraldehide-3 phosphate) form. G3P has the following structural formula:



I`m confused with the formation of NADH + (H+) from NAD+.
In 1,3-Bisphosphoglycerate formula I only see 1 hydrogen is missing. From where NAD+ takes another hydrogen to be reduced to NADH + H+?
As I know in order to form NADH + H+, NAD+ need to get 2 hydrogen atoms, i.e. 2 electrons and 2 protons. 2 electons along with 1 proton creates NADH and 1 proton of hydrogen atom (H+) goes to aqueous medium.

Thank you in advance,
Sam

[MrMistery]

I was 99% sure what the answer might be: the second hydrogen comes from the phosphate ion. Because your reaction has 2 reactants: G3P and a phosphate ion.
Just to be 100% sure I looked it up in my trusty Lehninger. My assumption was indeed correct.

[samoyan]

Thank you very much for your response! I really appreciate it!!!

I found an article on the net where there was a picture of phosphate ion with hydrogen atom attached, but I was still not sure about this.





I didn`t know 100% that inorganic phosphate (P-i) has hydrogen attached to one of its oxygen atoms. In almost all books, phosphate group is shown with only 1 phosphorus atom and 4 oxygen atoms. May be because it floats in cytosol it somehow attaches hydrogen atoms to one of its oxygens.

Thank you!

[samoyan]

Just to be 100% sure I looked it up in my trusty Lehninger. My assumption was indeed correct.

Do you mean this book? http://www.amazon.com/Lehninger-Princip ... 0716743396

[MrMistery]

yes that book. And the pictures you posted are from that book.

[victor]

I think that actually in aqueous solution, phosphate ion is in the form of HPO4(2-). Why HPO4(2-)? Well, it's because that ionization towards PO43- would create a stronger base compared to the H+ released from the HPO4(2-). So, the equilibrium would remains in HPO4(2-) rather in PO4(3-).

[samoyan]

Great conclusion, thank you!
Currently, I`m learning chemical equilibrium and ionization concepts in college. So, it`s a good stimuli to learn both chemistry and biology simultaneously.

[raghda]

in Harper's biochemistry ,you find that G3P isn't directly coverted to1,3 biphosphoglycerate .
through this indirect conversion hydrogen removed and carried on NAD+ and doesn't come from Pi