Industrial Biotransformations

60
2 The Enzyme Classification
in genetic engineering sciences, allowing the connection of two DNA strings to give a
single string.
To generalize, ligases are enzymes that catalyze a bond formation between two molecules.
This reaction is always coupled with the hydrolysis of a pyrophosphate bond in
ATP or a similar triphosphate. The bonds formed are, e.g., C–O, C–S and C–N bonds.
The systematic names should be formed by the system X:Y ligase.
EC 6.1 Forming carbon–oxygen bonds
R
tRNA OH + HO
+ ATP
NH2 P = diphosphate
R = organic residue
O
tRNA
O
O
R
NH 2
+ AMP
The tRNA-hydroxy group is the 2′-or3′-hydroxy group of the 3′-terminal nucleoside.
EC 6.2 Forming carbon–sulfur bonds
CoA
O
O
SH +
HO R
+ NTP
CoA
S R
+ NMP
P = diphosphate
R = organic residue
NTP = nucleotide triphosphate (ATP, GTP)
NMP = nucleotide monophosphate (AMP, GMP)
The thiol group is the terminal group of the coenzyme A (CoA) molecule.
EC 6.3 Forming carbon–nitrogen bonds
O O
+ HNR2 + ATP + AMP or ADP
R X R NR2 P = monophosphate, diphosphate
X = OH, H, COOH
R = hydrogen, organic residue
+
+
+ P
P
P