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    Maybe it's a stupid question, but what's the pH of pepsin and albumen? (Note: I'm not asking the optimum pH...) Thanks. I'm doing an essay on enzymes.
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    they are both proteins so Id guess theyd be neutral or thereabouts
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    they are probably at a pH around neutral as said above because pepesinogen is secreted when chyme enters the duodenum by the pancreas in pancreatic juice. Also the pancreatic juice also contain hydrogen carbonate ions which neutralise the acidic mixture comin from the stomach.


    Hope that helps and not very late
    Charles
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    Right, pH is a measure of the concentration of protons in a (I think it should be aqueous) solution. Thinking about it, these protons will be coming from the acidic and basic amino acid residues (the acidic ones donating protons, the basic ones accepting, as you'd expect), so the pH of a protein should be connected to the ratio and number of the acidic side groups to basic ones (more acidic ones lowering the pH from what I presume would originally be 7, from the water solvent, more basics ones meaning a >7 pH) and also on the various strengths of these groups.

    I think it's quite possible that the pH of these proteins would not be neutral. A google gives the isoelectric point of pepsin as pH2.7...But that's only when the protein's neutral - doesn't necessarily give a neutral pH.

    Hmm, I'm now lost. The best way would be to go purify some of your proteins and measure the pH :p:, but mebbe easier said than done.

    I dunno, possibly the size of an individual protein means that the proton-donating/accepting is negligible? It wouldn't seem that sensible for an organism that likes to be around pH7 to have proteins mucking it up... I dunno, it's interesting, I'll go look some more.
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    Albumin...Proteins don't really come at a pH as such - they change their form with the prevailing pH. They have a isoeletric point where they will be neutral but that is dependent on the pH of the solution they are in. I could put albumin into a highly acidic solution and it would act as a base etc etc (they can act as buffers in this way).

    For pepsin, again a protein, it would have an optimum pH (which is acidic in its case).

    What would the pH of a pure solution of albumin or pepsin? Probably around neutral because you'd get some balance in proton donors and acceptors...
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    (Original post by ixivxivi)
    Right, pH is a measure of the concentration of protons in a (I think it should be aqueous) solution.
    isnt pH a measure of H+ ions? hence potential Hydrogen... or is it a measure of both H+ ions and concentration of protons
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    (Original post by qin95)
    isnt pH a measure of H+ ions? hence potential Hydrogen... or is it a measure of both H+ ions and concentration of protons
    H+ ions are the same thing as protons

    As for the question of pH, I assume that the way you would have to figure that out is to take say a known solid mass of pepsin/albumin and then dissolve it in water and see what the ph is, however the actual ph of enzymes does not seem to be discussed too much as they are only assists in a chemical reaction, their response to their environment seems to be of more interest, but who knows? I wouldn't not want to assume away the swathes of biochem study on proteins and enzymes.

    However the point that was made about the isoelectric point of pepsin being ph2.7, that suggests that this H+ conc is needed to overcome what I assume is a high pkb for NH2 to accept protons, this would suggest that the protein is negatively charged beforehand and so therefore that it is donating H+ ions off its COOH groups to form COO- (sorry about lack of superscript) and so therfore the ph of pepsin dissolved in water would be somewhere below 7 as it will donate H+ ions in solution.

    However (again) the previous paragraph is a sketchy attempt at reasoning at something I don't know the answer to and so I would defineately appreciate someone setting me straight!
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    (Original post by Burnsey)
    However the point that was made about the isoelectric point of pepsin being ph2.7, that suggests that this H+ conc is needed to overcome what I assume is a high pkb for NH2 to accept protons, this would suggest that the protein is negatively charged beforehand and so therefore that it is donating H+ ions off its COOH groups to form COO- (sorry about lack of superscript) and so therfore the ph of pepsin dissolved in water would be somewhere below 7 as it will donate H+ ions in solution.
    yeah that sounds pretty plausible...
    add pepsin with IEP of pH 2.7 to a solution of pH 7, it wants adds protons, so it would but that brings the pH of the overall soution down, negating the driving force of proton contribution (because pepsin adjusts to the prevaling pH) - you probably get some kind of equilibrium with a pH just below 7
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    (Original post by Burnsey)
    However the point that was made about the isoelectric point of pepsin being ph2.7, that suggests that this H+ conc is needed to overcome what I assume is a high pkb for NH2 to accept protons, this would suggest that the protein is negatively charged beforehand and so therefore that it is donating H+ ions off its COOH groups to form COO- (sorry about lack of superscript) and so therfore the ph of pepsin dissolved in water would be somewhere below 7 as it will donate H+ ions in solution.
    Thanks for the help guys (even though it's a bit late as I've handed in my assignment weeks ago :rolleyes: )

    Anyways, I don't understand what IEP, pkb and what that sentence means. Could any one of you please explain it to me? Thanks.
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    pepsin is ph2 as it is a stomach acid so is acidic
 
 
 
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