Proteins(1) Flashcards
(31 cards)
the only common amino acid
that is not chiral
glycine
formed by enzyme-facilitated reaction
Derived amino acids
constituent of several proteins involved in
blood clotting.
γ-carboxyglutamic acid
presence of P regulates the activity
of proteins.
O-phosphoserine -
the amino acid sequence of the
polypeptide chain
primary structure
a result of covalent bonding between the amino acids
peptide bonds
translations of information contained in genes
Primary Structure
involves heating in the presence of 6N HCl in a sealed tube at 110oC for 10 – 100 hrs. depending on the nature of the peptide or protein to be hydrolyzed
* the protein is completely hydrolyzed, but trp is destroyed completely and ser, thr, and tyr are partially destroyed.
Acid Hydrolysis
- heating in the presence of 4N NaOH in a sealed tube at 10 – 100 hrs as in acid hydrolysis
- does not damage trp, but destroys arg, cys, cys-cys, thr, & ser; and some amino acids are partly deaminated
- more disadvantageous but since it does not destroy trp, it is used in the quantitative determination of this amino acid
Alkaline Hydrolysis
cleaves external peptide bonds
*Exopeptidases
- sequentially cleaves peptide bonds, beginning at the N- terminal end of the polypeptide.
- the liberated amino acids are identified one by one.
*Aminopeptidases
the polypeptide chain is reacted with 1–fluoro–2,4–dinitrobenzene (DNFB). The resultant dinitrophenyl-amino acid or DNP-amino acid can be separated from the other amino acids by ion–exchange chromatography after the polypeptide is hydrolyzed because it is more soluble in nonpolar solvents
Sanger’s method
uses phenylisothiocyanate (PITC),
(Edman’s reagent.) which combines with the N-terminal amino acid to yield a phenylthiohydantoin-compound (PTH-
compound). This can be identified by chromatography and extracted by organic solvent.
Edman degradation
preferentially cleaves peptide bonds when an aromatic amino acid is the C–terminal residue.
Carboxypeptidase A
cleaves basic amino acid residues. Because these enzymes sequentially cleave peptide bonds starting at the C–terminal residue, the first amino acid liberated is the C–terminal residue.
Carboxypeptidase B
reacts with all amino acids whose carboxyl group bis bound in peptide linkage, creating amino acylhydrazides. Only the C-terminal amino acid is spared.
Hydrazine method
-cleaves peptide bonds on the carboxyl side of the two strongly basic amino acids arg and lys.
Trypsin
cleaves peptide bonds on the carboxyl side of
the three aromatic amino acids (phe, tyr, and trp).
Chymotrypsin
cleaves on the carboxyl side of gly and ala
Elastase
cleaves peptide bonds at the amino end of aromatic amino acids (phe, trp, tyr), acidic amino acids (asp, glu) and ile
Pepsin
cleaves peptide bonds at the amino end of the
three aromatic amino acids, phe, tyr, trp; and amino acids with bulky nonpolar R groups, leu, ileu, and val.
Thermolysin
specifically cleaves peptide bonds on the carboxyl side of methionine residues
Cyanogen Bromide (CNBr)
most common type of secondary structure
a-Helix
between the R groups of nonpolar amino
acids that are hydrophobic
Van der Waals forces