Tuesday, 27 December 2016

biochemistry - Where is the H+ ion in this step of glycolysis coming from?


conversion of G3P to 1,3-bisphosphoglycerate (from Fundamentals of Biochemistry by Voet, 5th ed.)


In this step of glycolysis, I'm not seeing where the \ceH+ ion on the product side is coming from. It seems to me that the G3P's aldehydic H is replaced by phosphate, and that H is given to \ceNAD+ to make NADH. So where is the extra \ceH+ coming from?



Answer



Although texts such as Berg et al. tend to refer to inorganic phosphate, \cePi, as orthophosphate (\cePO43), the term inorganic phosphate is used because in aqueous solution at pH 7.6 several phosphate species exist, the predominant one being \ceHPO42. If this is regarded as \cePi, then it is the source of the \ceH+, and the equation balances.



Note added by David:


On checking I find, in contrast to Berg, Lehninger’s book defines \cePi as monohydrogen phosphate (\ceHPO42), and Fersht actually writes the equation of the reaction (16-1) with \ceHPO42 rather than \cePi.


No comments:

Post a Comment

evolution - Are there any multicellular forms of life which exist without consuming other forms of life in some manner?

The title is the question. If additional specificity is needed I will add clarification here. Are there any multicellular forms of life whic...