Journal
ACTA CHEMICA IASI
Volume 25, Issue 2, Pages 112-126Publisher
DE GRUYTER OPEN LTD
DOI: 10.1515/achi-2017-0011
Keywords
Protein analysis; Casein; Spectrophotometry; Copper ions
Categories
Funding
- Romanian Government (Partnership Project Metafore by UEFISCDI of Bucharest) [107/2014]
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In the present paper, the interaction between copper ions and proteins is presented, in order to elaborate a simple and rapid spectrophotometric assay of casein in milk. Under alkaline conditions, copper ions form the biuret complex with the proteins, which can be used in protein determination. Although very specific, the biuret method is less sensitive. Using insoluble copper phosphate, casein is able to extract copper ions, with which it forms the biuret complex, while either the complex or copper ions could be determined in the ultraviolet range. Indeed, an increased absorbance of biuret complex at 215 nm was found. Nevertheless, copper ions can be determined in UV as well, their concentration being proportional to that of casein. When used tetraglycine instead casein, mass spectrometric measurements at pH higher than 11 revealed the formation of complexes with many copper ions bound to each peptide bond-containing molecule. Nevertheless, on diluting the biuret solution the complex may dissociate leading to very complex UV spectra that should be further studied.
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