Biology Reference
In-Depth Information
process have been undertaken the last 20 years, and a brief review of these
is given below.
Structure of A
β
in Solution
Several different techniques have been used to study the secondary struc-
ture of monomeric A
β
in solution. Since A
β
has a strong tendency to poly-
merize into fibrils, it is crucial to keep A
in a monomeric form during
measurements. Moreover, there is a risk that the synthetic peptide con-
tains small aggregates that can initiate the polymerization process, and it
is important to use proper procedures for the preparation of a monomeric
starting material.
β
Circular Dichroism
Circular dichroism (CD) spectroscopy is a frequently used technique for
studying the secondary structure of proteins (Greenfield
et al
., 1996). All
common amino acids except for glycine are chiral, and therefore, a protein
will absorb left and right circularly polarized light differently. The absorp-
tion is dependent on the conformation, and the technique is useful for the
estimation of the secondary structure, i.e. the amount of
β
-sheet,
α
-helix,
β
-turn and random coil in proteins and peptides. The technique is rela-
tively easy to use and a protein concentration around 10
M is usually suf-
ficient for analysis, but it is not possible to obtain detailed information.
Earlier studies showed that A
µ
-sheet
conformation. However, if the peptide is carefully prepared, unordered
structures dominate. It is clear that the structure is affected by the solvent,
and in
β
to a large extent was present in a
β
-helix stabilizing solvents such as hexafluoroisopropanol (HFIP),
a mostly
α
α
-helical structure dominates.
Nuclear magnetic resonance spectroscopy
Nuclear magnetic resonance (NMR) spectroscopy can provide informa-
tion at the atomic level, but requires sophisticated equipment, higher
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