SAKAGUCHI REACTION
- an essential amino acid, has as a positively charged imidazole functional group
- the imidazole makes it a common participant in enzyme catalyzed reactions
- basis for the Quantitative determination of Histidine.
- a blue violet color by the bromination of histidine is a specific test for this amino acid . Other imidiazole derivative gives a negative
- the unprotonated imidazole is
nucleophilic and can serve
as a general base, while the
protonated form can
serve as a general acid
- the residue can also serve a role in
stabilizing the folded structures of proteins
- are group of organic compounds
sharing a common functional group
- guanidine group in arginine reacts
with the Sakaguchi reagent to form
a red-coloured complex.
- a test SPECIFIC FOR ARGININE
- it is positive for the amino acid containing the guanidine group in Arginine
- sakaguchi reagent is consist of
α-Naphthol and a drop of sodium hypobromite
NITROPRUSSIDE REACTION
- the protein or amino acid is boiled with strong alkali to split out sulfur as sodium sulfite, which is detected by addition of sodium lead, which causes the formation of brown to black lead sulfide
- principle: this is a test for the presence of sulfur-containing amino acids
- this reaction is a test for cystine and cysteine, but not for methionine,
which contains firm-binded sulfur.
- the nitroprusside test is specific
for cysteine, the only amino acid
containing sulfhydryl group (-SH)
- this group reacts with nitroprusside in the presence of excess ammonia. Apply this test cysteine, cystine and methionine.
- principle: sodium nitroprussides is reduced by compound containing free sulfhydryl group to a red colored compound
- this reaction is often used for the detection of cysteine and glutathione
UNOXIDIZED
SULFUR TEST