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The Modification of Tyrosine
Published in Roger L. Lundblad, Claudia M. Noyes, Chemical Reagents for Protein Modification, 1984
Roger L. Lundblad, Claudia M. Noyes
The reaction of chymotrypsinogen A with diazotized arsanilic acid has been investigated.6 Diazotization of arsanilic acid is accomplished by treatment of p-arsanilic acid with nitrous acid (0.55 mM sodium nitrite in 0.15 M HCl at 0°C). After adjustment of the pH to 5.5 with NaOH the reagent is diluted to a final concentration of 0.02 M. Reaction with chymotrypsinogen is accomplished in 0.5 M sodium bicarbonate buffer, pH 8.5 with a 20-fold excess of reagent at 0°C. The reaction is terminated by the addition of a sufficient quantity of aqueous phenol (0.1 M) to react with excess reagent. The extent of the formation of monoazotyrosyl and monoazohistidyl derivatives is determined by spectral analysis.4, 5 The extent of reagent incorporation is determined by atomic absorption analysis for arsenic. Tyrosine (~ 1.0 mol/mol) and lysine (~ 4 mol/mol) were the only amino acid residues modified to any significant extent under these reaction conditions. The arsaniloazo functional group provides a spectral probe that can be used to study conformational change in proteins. In this particular study, there was a substantial change in the circular dichroism spectrum during the activation of the modified chymotrypsinogen preparation by trypsin. It is of interest that the modification of chymotrypsinogen by diazotized arsanilic acid does not apparently affect either the rate of activation or amount of potential catalytic activity as judged by the hydrolysis of A/-benzoyl-L-tyrosine ethyl ester.
The Modification of Tyrosine
Published in Roger L. Lundblad, Claudia M. Noyes, Chemical Reagents for Protein Modification, 1984
Roger L. Lundblad, Claudia M. Noyes
The reaction of chymotrypsinogen A with diazotized arsanilic acid has been investigated.6 Diazotization of arsanilic acid is accomplished by treatment of p-arsanilic acid with nitrous acid (0.55 mM sodium nitrite in 0.15 M HCl at 0°C). After adjustment of the pH to 5.5 with NaOH the reagent is diluted to a final concentration of 0.02 M. Reaction with chymotrypsinogen is accomplished in 0.5 M sodium bicarbonate buffer, pH 8.5 with a 20-fold excess of reagent at 0°C. The reaction is terminated by the addition of a sufficient quantity of aqueous phenol (0.1 M) to react with excess reagent. The extent of the formation of monoazotyrosyl and monoazohistidyl derivatives is determined by spectral analysis.4,5 The extent of reagent incorporation is determined by atomic absorption analysis for arsenic. Tyrosine (~ 1.0 mol/mol) and lysine (~ 4 mol/mol) were the only amino acid residues modified to any significant extent under these reaction conditions. The arsaniloazo functional group provides a spectral probe that can be used to study conformational change in proteins. In this particular study, there was a substantial change in the circular dichroism spectrum during the activation of the modified chymotrypsinogen preparation by trypsin. It is of interest that the modification of chymotrypsinogen by diazotized arsanilic acid does not apparently affect either the rate of activation or amount of potential catalytic activity as judged by the hydrolysis of N-benzoyl-l-tyrosine ethyl ester.
Current and emerging trends in point-of-care urinalysis tests
Published in Expert Review of Molecular Diagnostics, 2020
Rongwei Lei, Rannon Huo, Chandra Mohan
Other dipstick-based urinalysis tests are widely used as well. Reaction between sodium nitroprusside, acetoacetic acid, and acetone can yield a violet color, which can be used to detect ketones. To detect nitrite, the reaction between it and p-Arsanilic acid is used to form a diazonium compound, which couples with a quinolone compound to produce a pink color. Color change from orange to turquoise is indicative of a pH shift. Lastly, the Ehrlich Aldehyde reaction and a bilirubin and diazonium salt reaction are used to yield an azo red compound, which can be used to detect urobilinogen and bilirubin in the urine [40].