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704 Chapter 21
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exopeptidase
an enzyme that hydrolyzes a peptide bond at the end of a polypeptide chain.
fibrous protein
a water-insoluble protein; its polypeptide chains are arranged in bundles.
globular protein
a water-soluble protein; it tends to have a roughly spherical shape.
A
-helix
the backbone of a polypeptide coiled in a right-handed spiral with hydrogen
bonding occurring within the helix.
hydrophobic interactions
interactions between nonpolar groups. These interactions increase stability by
decreasing the amount of structured water, thereby increasing entropy.
interchain disulfide bridge
a disulfide bridge between two cysteine residues in different polypeptide chains.
intrachain disulfide bridge
a disulfide bridge between two cysteine residues in the same polypeptide chain.
ion-exchange
a technique that uses a column packed with an insoluble resin to separate
chromatography
compounds on the basis of their charge and polarity.
isoelectric point (pI)
the pH at which there is no net charge on an amino acid.
kinetic resolution
separating enantiomers based on the difference in their rate of reaction with an
enzyme.
loop conformation
see coil conformation.
(coil conformation)
N-terminal amino acid
the terminal amino acid of a polypeptide (or protein); it has a free amino group.
oligomer
a protein with more than one polypeptide chain.
oligopeptide
3 to 10 amino acids linked by amide bonds.
paper chromatography
a technique that separates amino acids based on polarity.
parallel
B
-pleated sheet
a type of secondary structure in which the adjacent hydrogen-bonded polypeptide
chains in a
b
-pleated sheet run in the same direction.
partial hydrolysis
a technique that hydrolyzes only some of the peptide bonds in a polypeptide.
peptidase
an enzyme that catalyzes the hydrolysis of a peptide bond.
peptide
a polymer of amino acids linked by amide bonds.
peptide bond
the amide bond that links the amino acids in a polypeptide or protein.
B
-pleated sheet
a type of secondary structure in which the backbone of a polypeptide extends in a
zigzag structure with hydrogen bonding between neighboring chains.