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I'm trying to model the transport of lactate in cells (in both direction via Monocarboxylate transporters):

[Lactate]intra + [H+] <----> [Lactate]extra + [H+]

I found some data on kinetics of Lactate itself (Km and Vmax) but I don't find anything on [H+].

My initial thought was to consider [H+] as a substrate, and model the transport as a sequential ordered Bi-Bi reversible reaction (from this paper: Poole & Halestrap (1993). Transport of lactate and other monocarboxylates across mammalian plasma membranes. doi:10.1152/ajpcell.1993.264.4.c761)

But it require a lot of parameters (Ki, Km, Vmax) for each substrate involved (especially H+).

So my question is: Should I consider [H+] as a substrate or just as an external parameter that impact the direction of the flux ?

Thanks everyone

(first question on Stackexchange)

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To include or exclude the H+ basically depends on the scope of your model. The H+ can be used as external parameters if you assume that both sides of the membrane are well buffered and the pH will not change. If you want to simulate a condition during which the pH changes, like for example strong exercise in muscle or ischemia, then you would need separate H+ for each side of the membrane.

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  • $\begingroup$ Thank you for your answer. Yes the pH will change at each side of the membrane (I simulate cancer cells with high glycolytic activity). But if I consider H+ as a substrate like lactate, should it follow a michaelis-menten kinetic (or derivatives) ? If so do you have any idea of where I can find this information about H+ ? I didn't find any paper measuring such parameters for H+. $\endgroup$ – Peepan Jun 4 '20 at 8:29
  • $\begingroup$ I think this article can give you some kinetic data on proton symporters with different pH. There is a lot published on the subject but it is difficult to find the best search term... perhaps this paper or this paper may also give some usefull parameters. $\endgroup$ – Lobostrous Jun 4 '20 at 13:01
  • $\begingroup$ Thank you ! I already downloaded the second article but didn't saw Km values for H+, a second read is usefull :) The cell's paper seems really promising, I'm going to read this right away. $\endgroup$ – Peepan Jun 4 '20 at 13:15

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