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Testing for Proteins


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#1 kabdoun

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Posted 7 February 2013 - 02:42 PM

I want to ask about the structural integrity of protein molecules that are present in mammalian bodily fluids. My question is not about the detection or determining what type of mammal has left a "protein fingerprint", but rather about the proteins that are left.

For how long can those proteins' structure stay without being compromised after being exposed to the outside world/environment? For how long can you test for these proteins before they are no more, if they actually lose their structure?


Edited by kabdoun, 7 February 2013 - 03:34 PM.

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#2 CharonY

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Posted 7 February 2013 - 05:17 PM

Depends a lot on the the protein and the environment. Some are inherently more stable than others, but degradation due to external factors weigh in heavily. Relevant parameters include the liquid composition it is in, temperature, presence of other enzymes etc.

 

It also depends a bit on what you mean by lose their structure. The tertiary structure is for the most part relatively unstable, at RT and without specific buffers most will readily lose their active confirmation (again, with some exceptions). But the proteins are still present and may be detectable (if inactive).


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#3 kabdoun

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Posted 7 February 2013 - 09:12 PM

So you are saying that I can't test for proteins present in mammalian bodily fluids if they are exposed to the environment for months as they disintegrate? Do they turn into dust?

 

Do they lose their liquid composition?


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#4 CharonY

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Posted 7 February 2013 - 09:59 PM

I do not know what you mean to liquid composition, and no, they do not turn into dust. Dust is comprised of extremely large particles, much larger than any single protein. Instead, proteins get degraded over time. Tertiary structure (and hence function) can get lost very fast, further degradation depend a lot on the environment. The quickest degradation is generally due to protease functions.


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#5 BabcockHall

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Posted 7 February 2013 - 10:25 PM

CharonY,

 

I agree.  I would just like to add that proteins sometimes denature by unfolding, but sometimes the suffer covalent change, such as proteolysis.  I think each protein has to be judged on a case-by-case basis.


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#6 LondonDispersion

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Posted 7 March 2013 - 03:00 PM

CharonY,

 

I agree.  I would just like to add that proteins sometimes denature by unfolding, but sometimes the suffer covalent change, such as proteolysis.  I think each protein has to be judged on a case-by-case basis.

 

Proteolysis, the breaking of covalent bonds, and proteases all go hand in hand.  Proteolysis would require proteases to facilitate hydrolysis and break the peptide bonds in the protein.  Hence CharonY is correct in saying, "The quickest degradation is generally due to protease functions." and I would add most common.

My input to this thread would be to not forget how susceptible proteins are to heat and pH because of their many H bonds.


Edited by LondonDispersion, 7 March 2013 - 03:01 PM.

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#7 BabcockHall

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Posted 7 March 2013 - 04:49 PM

The covalent changes I had in mind were not limited to proteolysis.  I was also thinking of oxidation of a methionine residue to a methionine sulfoxide, for example.  Asparagine residues can undergo certain changes as well, but I don't have a citation handy.  These covalent changes are somewhat different from noncovalent changes brought about by heating or other means.  Some (but not all) unfolding events are reversible; many of the covalent changes are not reversible. 


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