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Thread: Testing for Proteins

  1. #1 Testing for Proteins 
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    I have this identical thread on the subject but I was not sure whether to ask a biologist or a chemist about this since technically this is a question about Biochemistry

    So:
    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?


    Last edited by kabdoun; February 7th, 2013 at 09:38 AM. Reason: Sounded weird at first :D
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  3. #2  
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    There are various factors, as one might guess. Proteins maintain their structure while in their "biological conditions" (for example, ~pH 7 and ~37C and aqueous). Change those conditions, and your proteins will "denature" (become misshapen, sometimes permanently).

    You can readily see proteins in birds' eggs denature when heated to a high temperature, but such high temps aren't usually necessary. This denaturing is not reversible.

    You can also see proteins in milk denature when you put both milk and lemon juice in your tea (as famed theoretical physicist Richard Feynman almost ended up doing in his autobiog "Surely you're joking Mr Feynman", the book title being what the hostess nervously said regarding his request.) PS you don't need to use tea or acidy lemon juice, just dump some vinegar into the milk.

    As for losing aqueous environment, I'm sure dehydrating a protein solution (such as milk) can cause denaturing of the proteins (although a known example doesn't readily come to mind). If the milk albumin denatures, then it probably "re-natures" itself when rehydrated, because I've used rehydrated NFDM (Non-Fat Dry Milk) in experiments where the albumin needed to behave as it originally did.


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    But the structural integrity of the protein itself is lost by itself if exposed to room temperature? Without the application of further heating or cooling inputs? So in essence the protein denatures naturally if just left there?

    If so what does it turn into? Dust?
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    Protein stability varies wildly. Regulatory enzymes are often very unstable, while structural proteins can be very stable (collagen fragments have been discovered in fossilised dinosaur bones, for example). In the lab proteins may be stored reliably (under the right conditions) for just minutes, hours or days to years. Once out of their native environment proteins may lose their tertiary and secondary structures, chemical agents may bind to them, they may aggregate with other proteins, undergo UV photolysis, undergo various oxidation reactions or be digested by bacterial proteases.


    Here's a paper studying amylase activity in semen and saliva stains: http://projects.nfstc.org/workshops/...a%20Stains.pdf


    Amylase is quite a stable enzyme. From the results, the author sees little or no enzymatic activity after a couple of days (semen stain) to over a hundred days (saliva stain).


    I don't know enough about the topic be too much more specific than this. I think the take home message would be that it all depends on the protein of interest and the environment from which the sample is taken.
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    Ok that make sense... here is being more specific regarding the table you gave me... are there that much different types of proteins present in semen/pre-seminal stains?
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    What does denature mean? When proteins lose their structure they denature... Where do the components of the protein go? Do they stay where they are left and can we test for them?
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    A protein is said to denature when it loses its tertiary and secondary structure (overall shape and local shape). Think of a ball of string that has become unwound.

    You can certainly test a sample for the presence of proteins when the proteins are denatured. Identifying the proteins would probably be a lot more difficult.
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  9. #8  
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    and for how long can they be tested for? I mean is there a maximum amount of days?
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  10. #9  
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    One way to understand this is to think about virus, A virus is essentily a naked piece of protein. The common cold viruses can lay around on environmental surfaces for days and remain infectious, the HIV virus, the one responsible for AIDS, is denatured and rendered no longer infectious, by about one minute of exposure to air.
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  11. #10  
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    But it is still there?
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  12. #11  
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    Yes. For hours, days, weeks, months. years, centuries, millenia or eons depending on the particular environmental circumstances.
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