Hopkins–Cole reaction

The Hopkins-Cole reaction, also known as the glyoxylic acid reaction, is a chemical test used for detecting the presence of tryptophan in proteins.[1] A protein solution is mixed with Hopkins Cole reagent, which consists of glyoxylic acid. Concentrated sulfuric acid is slowly added to form two layers. A purple ring appears between the two layers if the test is positive for tryptophan.[2][3] Nitrites, chlorates, nitrates and excess chlorides prevent the reaction from occurring.[4]

The reaction was first reported by Frederick Gowland Hopkins and Sydney W. Cole in 1901,[5] as part of their work on the first isolation of tryptophan itself.

References

1. R.A. Joshi (2006). Question Bank of Biochemistry. New Age International. p. 64. ISBN 978-81-224-1736-4.
2. Debajyoti Das (1980). Biochemistry. Academic Publishers. p. 56. ISBN 978-93-80599-17-5.
3. P. M. Swamy (2008). Laboratory Manual on Biotechnology. Rastogi Publications. p. 90. ISBN 978-81-7133-918-1.
4. Chatterjea (1 January 2004). Textbook of Biochemistry for Dental/Nursing/Pharmacy Students. Jaypee Brothers Publishers. p. 51. ISBN 978-81-8061-204-6.
5. Hopkins, Frederick Gowland; Cole, Sydney W. (1901). "On the proteid reaction of Adamkiewicz, with contributions to the chemistry of glyoxylic acid". Proceedings of the Royal Society. 68 (442–450): 21–33. doi:10.1098/rspl.1901.0008. S2CID 84899015.