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Topic: How to determine protein presence?  (Read 6388 times)

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  • Guest
How to determine protein presence?
« on: June 24, 2005, 08:03:38 AM »
Hi, I'm looking for a relatively basic method to determine if a sample contains a significant amount of protein.  I have thought of Kjeldahl for total nitrogen or via a.a.  Is there a simpler method?  Is there an enzyme that would break the proteins up and then I could test for specific amino acids?



  • Guest
Re:How to determine protein presence?
« Reply #1 on: June 24, 2005, 06:27:59 PM »
If protein is present:

Sample + Benedict's + Heat = Purple

Sample + Biuret + Heat = White precipitate

I don't know how far you can go with that, but that's just basic detection.
« Last Edit: June 24, 2005, 06:29:04 PM by arnyk »


  • Guest
Re:How to determine protein presence?
« Reply #2 on: June 25, 2005, 10:39:29 PM »
If you want to quantify protein and you have a spec:

1) Bradford Dye - pretty easy to do and cheap

some other ones - I've not used just done once a long time ago
2) Lowry assay
3) Smith assay

If you have a good spec - you would need it to have UV capabilities and a quartz curvette.

A280 = 1 A (mL/cm mg) x [Conc.] (mg/mL) x 1 (cm)

Using UV absorption can be tricky - has to be a pure sample (free from other UV absorbing substances) and different proteins will absorb differently.  Some people use A205.  

The Bradford assay is just using Coomassie Blue dye.  It is okay but has problems with detergents and sometimes can be tricky due to the proteins.  For example, one lab I was in used a animal protein for it's standard curve and we were testing for levels of a plant protein.  That's not the best.  For the best results, standard and test variable should be the same.

The Lowry and smith assays are both good, but a little time consuming to set up.  I also think they are time dependant (can't remember ).

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