Color Reactions of Proteins

Test Ninhydrin

Color Reactions of Proteins Composition of + Result Grp. Responsible Reagent Triketohydrin Hydrate Lavander Free amino and free COOH

Importance Test for a.a. peptides in determining amino acids + to tripeptides up to protein + to tryptophan

Biuret

NaOH + CuSO4

Violet

Peptide linkages

Millon’s

Hg in HNO3

Red

Xanthroproteic

Conc. HNO3

Lemon yellow

Hydroxyphenyl group Benzene ring

Hopkins-Cole

Glyoxylic acid and conc. H2SO4 Conc HCl , sucrose Pb(OAc)2 Sullfanilic acid in HCl NH4OH 10% NaOH, ά naphtol, alkaline hypobromite HCHO conc. H2SO4

Violet ring

Indole group

+ trp

Violet Red orange – lighter orange

Indole group

+ trp + his and tyr

Liebermann Erlich’s Diazo Sakaguchi AcreeRosenheim Reduced Sulfur Br water Molisch Adamskiewez

+ Tyr, Phe, Trp

Intense red color Guanidine

+ arginine

Violet ring

Indole group

+trp

KOH, Pb(OAc)2

Black ppt

Sulfur

Br.H2O, amyl alcohol ά naphtol in alcoholic H2SO4 Glacial HOAc and conc. H2SO4

Pink Violet ring

Indole group Carbohydrates

+ cystine, Cystein and methionine + trp Glycoprotein

Reddish violet ring at the junction

Indole group

+ trp

Test for Carbohydrates Test Composition of Reagent Molisch ά naphtol in alcoholic H2SO4

+ Result Purple ring

Importance Gen. Test for carbohydrates Test for ketoses Test for pentoses Test for galactose and lactose Test for polysaccharides; differentiate from helical polyssacharide

Seliwanoff Bial’s Mucic

Resorcinol in HCl Orcinol in HCl Conc. HNO3

Iodine test

Iodine in KI

Red color + brown ppt Blue green White ppt / colorless / red –like crystals Deep blue –starch Purple –amylodextrin Red- erythrodextrin Colorless – achroodextrin Mahogany red – inulin

Osazone

Phenylhydrazine + NaOAc

Yellow ppt

Barfoed’s

Cu(OAc)2, HOAc

Brick red ppt

Benedict’s

CuSO4, Na2CO3, Sodium citrate (not strongly alkaline) Bismuth subnitrate + KOH + Rochelle salt AgNO3 + x’ss NH3 NaOH

Brick red ppt of Cu2O

Test to identify sugars in microscopic appearance Distinguish mono from disaccharides Test for reducing sugars

Black ppt of Bi

Test for reducing sugars

Silver mirror Caramel odor, brown color

Test for reducing sugars Test for reducing sugar

Nylanders Tollen’s Moore’s