Amino acids and proteins. Dr Una Fairbrother. Amino acids and proteins. Proteins are composed of amino acids When a protein is hydrolysed e.g. with hydrochloric acid then about 20 different amino acids can be detected
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Two of the aromatic amino acids, tryptophan and tyrosine are useful in quantitative protein determination.
They are detected in the Lowry assay: a biochemical test to measure the amount of protein in a sample.
Copper(II) ion in alkaline solution reacts with protein to form complexes, which react with a Folin-phenol reagent. The product becomes reduced and can be detected colourimetrically by absorbance at 650 nm.
The curve produced is really two curves added together. On the left-hand side is the curve from the titration of the carboxyl group. On the right-hand side is the curve from the titration of the amino group.
One equivalent of NaOH is required to titrate each acidic group.
When the first equivalent has been added the amino acid is in its dipolar form.