There are different types of protein assays which are used
in finding the concentration of proteins, but not all of them produce accurate
results (Sim, Suderio & Teope, 2008).
The method which is the only method to produce accurate and reliable
results is by taking a portion of a protein assay sample and acid hydrolysing
it, after which you then carry out amino acid analysis on the hydrolyzate. As
much as this method is an accurate one, it is also very time consuming which is
why it is not used very often.
The assay which are used mostly in analysing the protein
concentration are the Folin-Lowry assay, Bicinchoninic Acid assay, the UV
absorbance and the Bradford assay. The Lowry assay works by complexing copper
with nitrogen in the protein and the complexed tyrosine and tryptophan is then
reacted with Folin-Ciocalteu phenol reagent. This then gives an intense,
blue-green colour, which absorbs at 650-750 nm (Cartwright, 2017).
With the BCA it works in a similar way to the Lowry assay,
as the protein is complexed with copper ions. The only difference is that the
copper bound protein binds to BCA to
give a deep purple colour. The purple colour is proportional to the amount of
protein present in the solution. The UV Absorbance oversees the absorbance of
amino acids, such as tyrosine and tryptophan. The advantage of this process is
that it is fast with samples that can be retrieved , but often contaminated by
buffers, biological materials and salts (Sim, Suderio & Teope, 2008).
The Bradford assay is one of the most popular procedures
used in measuring protein concentration in a protein solution (Cheng, Wei, Sun,
Tian & Zheng, 2016). One of the great things about the Bradford protein
assay is that it has an easy protocol to follow, although some ingredients in
protein drugs mostly detergents often disrupt the Bradford assay even at low
The good thing is that there are processes which can be done
to avoid things such as sample errors within the assay, and the best way to
achieve this is by assaying the protein after it has been diluted in several
fold in a compatible buffer (Cheng, Wei, Sun, Tian & Zheng, 2016). This is
because this process will decrease the number of interfering substance within
the sample to a lower level where it no longer disrupts the assay.
The Bradford assay involves the use of a Coomassie dye is
required, as this what the protein binds to and while under acidic conditions, a
reaction occurs which changes the dye from a brownish colour to blue. The
Bradford method measures the presence of standard amino acids residues such
as arginine, lysine as well as histidine