2-Vinylquinoline, a reagent to determine protein sulfhydryl groups spectrophotometrically |
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Authors: | L H Krull D E Gibbs M Friedman |
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Institution: | Northern Regional Research Laboratory2, Peoria, Illinois 61604 USA |
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Abstract: | A reagent has been sought for the selective derivatization of protein sulfhydryl groups that will allow the spectrophotometric determination of the cysteine and cystine content of intact proteins. 2-Vinylquinoline appears to be that reagent. Protein sulfhydryl groups were reacted with 2-vinylquinoline to yield the protein-linked S-2-(2-quinolylethyl)-l-cysteine (Qe-cysteine). After urea and other excess reagents were removed, the modified proteins were examined spectrophotometrically. The extinction coefficient (10,000) and absorption maximum (318 mμ) of the protein-linked vinylquinoline derivatives were identical to those of the model Qe-cysteine. Optimum conditions for the reaction require an equimolar concentration of 2-vinylquinoline to all sulfhydryls and a 4 hr reaction period. The total cysteine and cysteine contents of the proteins, when determined under these conditions, were in excellent agreement with standard literature values. |
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