178 Part II: Water, Enzymology, Biotechnology, and Protein Cross-linking
Table 8.1.(Continued)
Asparagine Asn (N)Glutamine Gln (Q)Serine Ser (S)Threonine Thr (T)Cysteine Cys (C)Tyrosine Tyr (Y)Negatively Charged Amino Acids
Glutamate Glu (E)Aspartate Asp (D)Positively Charged Amino Acids
Arginine Arg (R)Lysine Lys (K)Histidine His (H)oxygen of the carbonyl group and the hydrogen of
the NH group are in the transposition; the ciscon-
formation occurs only in exceptional cases (Rich-
ardson 1981).
Enzymes have several “levels” of structure. The
protein’s sequence, that is, the order of amino acids,
is termed as its primary structure. This is deter-
mined by the sequence of nucleotide bases in the
gene that codes for the protein. Translation of the
mRNA transcript produces a linear chain of amino
acids linked together by a peptide bond between
the carboxyl carbon of the first amino acid and the
free amino group of the second amino acid. The first
amino acid in any polypeptide sequence has a free
amino group, and the terminal amino acid has a free
carboxyl group. The primary structure is responsible
for the higher levels of the enzyme’s structure and
therefore for the enzymatic activity (Richardson
1981, Price and Stevens 1999).The Three-Dimensional Structure of EnzymesEnzymes are generally very closely packed globular
structures with only a small number of internal cavi-
ties, which are normally filled by water molecules.
The polypeptide chains of enzymes are organized
into ordered, hydrogen-bonded regions, known as
secondary structure (Andersen and Rost 2003). In
these ordered structures any buried carbonyl oxygen
forms a hydrogen bond with an amino NH group.