The Hopkins-Cole reaction, also known as the glyoxylic acid reaction, is a
chemical test used for detecting the presence of
tryptophan in proteins. A protein solution is mixed with Hopkins Cole reagent, which consists of
glyoxylic acid. Concentrated
sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...
is slowly added to form two layers. A purple ring appears between the two layers if the test is positive for tryptophan.
Nitrite
The nitrite polyatomic ion, ion has the chemical formula . Nitrite (mostly sodium nitrite) is widely used throughout chemical and pharmaceutical industries. The nitrite anion is a pervasive intermediate in the nitrogen cycle in nature. The name ...
s,
chlorate
The chlorate anion has the formula ClO3-. In this case, the chlorine atom is in the +5 oxidation state. "Chlorate" can also refer to chemical compounds containing this anion; chlorates are the salts of chloric acid. "Chlorate", when followed by ...
s,
nitrate
Nitrate is a polyatomic ion
A polyatomic ion, also known as a molecular ion, is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zer ...
s and excess
chlorides prevent the reaction from occurring.
The reaction was first reported by
Frederick Gowland Hopkins and
Sydney W. Cole in 1901,
as part of their work on the first isolation of tryptophan itself.
References
Protein methods
Chemical tests
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