analysis and denaturation of proteins

• Hopkins Cole Test

  the color of ring is blue/violet if positive
• Hopkins cole test used to detect the presence of tryptophan
• in hopkins cole test, the aldehyde group react with the indole ring
• we used Albumin, Gelatin, tyrosine, and tryptophan in hopkins cole test as samples
• the reagents in hopkins cole test are magnesium glyoxylate and sulfuric acid
• Biuret test used to detect the presence of peptide bonds
• biuret test has the principle of: cupric ions form a complex with nitrogen atoms in peptide bonds found in protein
• biuret test uses 3 samples, these are: albumin, alanine and urea
• biuret test is reagent made up of NaOH, and CuSO4
• in biuret test, if the sample is positive it will show you a color of purple
• in biuret test if negative, it will show you a blue color sample which means it has only amino acids and dipeptides
• in biuret test, alanine and urea tested negative
• ninhydrin test is used to detect the presence of amino groups
• in ninhydrin test, if the sample tested positive it will show you 2 possible complexes. 1st is blue/violet complex if amino acids are present and yellow complex if (hydroxy) proline is present
• xanthoproteic test used to detect aromatic ring
• in xanthoproteic test, the nitration of amino acid will yield to nitrobenzene
• xanthoproteic test reagent have nitric acid + heat
• in xanthoproteic test, the positive sample will show a yellow precipitate: Tyrosine, Phenylalanine, tryptophan
• Millon's test used to detect the presence of tyrosine
• millon's test principle: the nitrification of phenyl group in tyrosine will yield to a formation of complex with mercury
• millon's test reagent have: mercuric nitrate, mercurous nitrate, and concentrated HNO3
• in millon's test if it tested positive it will show a red/pink precipitate meaning mercury complex of nitrophenyl derivatives
• Lead acetate test is used to detect the presence of sulfur containing amino acid
• lead acetate reagent have NaOH, lead acetate + heat
• inorganic sulfide react with lead acetate resulting in lead sulfide
• in lead acetate test if positive, it will show you a black/brown precipitate. meaning it has cysteine and methionine
• cysteine and methionine is detected in lead acetate test
• tyrosine, phenylalanine, and tryptophan can be detected using xanthoproteic test
• Hopkins cole, xanthoproteic, millon's, and lead acetate test are the test we did during laboratory
• coagulation due to heat will disrupt the hydrogen bonds because it causes to vibrate and to move rapidly
• coagulation due to inorganic acid (HCl) the changes in ph can disrupt the H bonding and Salt bridges
• coagulation due to alcohol (ethanol)- has the capability to engage in intramolecular H bonds. it disrupts the H bonds, and r-group in a protein
• Precipitation due to heavy metal (lead, silver, and mercury)
• carboxylate anion disrupt the salt linkages
• -SH group in cysteine disrupt the disulfide linkages
• precipitation due to alkaloidal reagents (tannic acid)

  reagents when combine in positively charge amino groups can disrupt salt linkages