Introduction to Enzyme and Coenzyme Chemistry - E-Library Home

16 Chapter 2
(a)
(b)
Figure 2.12 Structure of two anti-parallel b-sheets, (a) showing positions of the polypeptide chain
and side chains and (b) showing the same structure in ribbon format.
The b-turn is a structure often formed at the end of a b-sheet which leads to
a 180 8 turn in the direction of the peptide chain. An example of a b-turn is
shown in Figure 2.13, where the role of hydrogen bonding in stabilising such
structures can be seen.
2.6 The folded tertiary structure of proteins
The three-dimensional structure of protein sub-units, known as the tertiary
structure, arises from packing together elements of secondary structure to
form a stable global conformation, which in the case of enzymes is catalytically
active. The packing of secondary structural units usually involves burying
R
O
N
R
H
N
H
O
R
N
O
H
N
C
R
Figure 2.13 Structure of a b-turn.