[Helen]

Hi everyone, first post probably of many.
 
Does the Folin and biuret methods both produce the same mg/ml results ?


Thank you

[Arkcon]

Yes.  Except when not.  Unless.  If.

Sorry for the flippant answers, but you've left some steps out.  Briefly, they rely on different reactions at slightly different wavelengths, so you should expect a slightly different response.  Each individual protein behaves differently in each case.  Compared to a standard curve of the same protein, you should get a similar answer, or maybe the same result, within whatever statistical variation you're capable of working with.

But we need a more complete question, to give you a good answer.  If you have an unknown solution of protein, and you cook it up each way and just want an accurate answer, then no, this isn't likely to work.  But you shouldn't do it that way in any case.

[Helen]

Thank you for replying, and sorry for the short question i am a complete novice when it comes to analytical chemistry.
i have been asked to determine the unknown concentration of protein using the biuret and folin methods, i have researched the differences between these two methods but can not seem to understand what the results should be, complete brain fried.
both the biuret and folin method used 400µl of x and y protein but the folin x and y had been diluted /20
absorbance for biuret was set at 550nm and the folin 660nm
im struggling with the write up as i really don't have a clue each of the results should have been

ok so ive calculated the SD and the SEM
Biuret, X is SD 0.008 and SEM 0.005 and Y  SD 0.007 and SEM 0.004
Folin, X/20 is SD 0.008 and SEM 0.005 aand Y SD 0.005 and SEM 0.003
does this make sense
Thanks again

[Arkcon]

You should just report what you've found.  It may be absolutely correct or totally wrong.  You appear to have compensated for the different dilutions correctly, so there's not much more to do.  You know they rely on different chemistry, so that can explain why the response is different.  FWIW, if you do a protein assay, you always mention which one you used when reporting the concentration.

Although you should also generate a standard curve from a known standard protein, such as BSA.  But if that's not part of your experimental plan, then you can just do without it.  That's just some info for you on how we try to standardize procedures.

[Babcock_Hall]

When the biuret, Lowry, and Bradford (as kitted by BioRad) were compared, two things are apparent.  One is that there is great protein-to-protein variation.  The other is that there is no obvious correlation between how a protein will do in one assay versus how it will do in another, although I may detect a slight correlation between the biuret and Lowry assays.  One conclusion that I would draw from this table is that if you use, for example, bovine albumin as your standard and are quantitating a different protein, you may obtain concentrations with a systematic error.
http://www.bio-rad.com/LifeScience/pdf/Bulletin_9004.pdf

[Helen]

Thank you all, i did a bit more research on both protein assay methods so as to better understand the experiment and results.

can any of you ever remember thinking that you would never get chemistry and maths ? or does it just come naturally to budding scientists ? im desperate to learn but it just doesn't seem to sink in 
schedule suggests that the folin and biuret results should similar
Final calculations are Biuret 3.1mg/ml and 6mg/ml
                              Folin 4mg/ml and 4mg/ml
are the biuret results too far out to be seen as similar do you think ??