reservoir of biocatalysts still remains to be discovered and is waiting to be used.
However, only a minor fraction of the enzymes already investigated (~10%) is
commercially available. However, this number is steadily increasing.
For identification purposes, every enzyme has a four-digit number in the general
form [EC A.B.C.D], where EC stands for ‘Enzyme Commission’. The following
properties are encoded:
A. denotes the main type of reaction (see Table 1.5);
B. stands for the subtype, indicating the substrate class or the type of transferred
molecule;
C. indicates the nature of the co-substrate;
D. is the individual enzyme number.
As depicted in Table 1.5, enzymes have been classified into six categories
according to the type of reaction they can catalyze. At first glance, it would seem
advantageous to keep this classification throughout this book, since organic chemists
are used to thinking in terms of reaction principles. Unfortunately, this does not work
in practice for the following reasons: Due to the varying tolerance for nonnatural
substrates, the importance for practical applications in organic synthesis is not at all
evenly distributed amongst the different enzyme classes, as may be seen from the
‘utility’ column in Table 1.5 (compare Chap. 4). Furthermore, due to the widespread
use of crude enzyme preparations (containing more than one active biocatalyst), one
often does not know which enzyme is actually responsible for the biotransformation.
Last but not least, there are many useful reactions which are performed with whole
microbial cells, for which it can only be speculated as to which of the numerous
enzymes in the cell is actually involved in the transformation.
Table 1.5 Classification of enzymes
Enzyme class
Number
Reaction type
Utility
a
Classified Available
1. Oxidoreductases ~2000
~100
Oxidation/reduction: oxygenation of C–H,
C–C, C¼C bonds, or overall removal or
addition of hydrogen equivalents
+++
2. Transferases
~1900
~100
Transfer of groups: aldehydic, ketonic,
acyl, sugar, phosphoryl, methyl, NH 3
++
3. Hydrolases
~1700
~200
Hydrolysis/formation of esters, amides,
lactones, lactams, epoxides, nitriles,
anhydrides, glycosides, organohalides
+++
4. Lyases
~700
~50
Addition/elimination of small molecules
on C¼C, C¼N, C¼O bonds
++
5. Isomerases
~250
~10
Isomerizations: rearrangement,
epimerization, racemization, cyclization
+
6. Ligases
~200
~10
Formation/cleavage of C–O, C–S, C–N,
C–C bonds with concomitant triphosphate
cleavage
Æ
a
The estimated utility of an enzyme class for the transformation of nonnatural substrates ranges
from +++ (very useful) to Æ (little use) [144]. (Based on the biotransformation database of Kroutil
and Faber (2016) ~17,000 entries.)
1.4 Enzyme Properties and Nomenclature
21
However, only a minor fraction of the enzymes already investigated (~10%) is
commercially available. However, this number is steadily increasing.
For identification purposes, every enzyme has a four-digit number in the general
form [EC A.B.C.D], where EC stands for ‘Enzyme Commission’. The following
properties are encoded:
A. denotes the main type of reaction (see Table 1.5);
B. stands for the subtype, indicating the substrate class or the type of transferred
molecule;
C. indicates the nature of the co-substrate;
D. is the individual enzyme number.
As depicted in Table 1.5, enzymes have been classified into six categories
according to the type of reaction they can catalyze. At first glance, it would seem
advantageous to keep this classification throughout this book, since organic chemists
are used to thinking in terms of reaction principles. Unfortunately, this does not work
in practice for the following reasons: Due to the varying tolerance for nonnatural
substrates, the importance for practical applications in organic synthesis is not at all
evenly distributed amongst the different enzyme classes, as may be seen from the
‘utility’ column in Table 1.5 (compare Chap. 4). Furthermore, due to the widespread
use of crude enzyme preparations (containing more than one active biocatalyst), one
often does not know which enzyme is actually responsible for the biotransformation.
Last but not least, there are many useful reactions which are performed with whole
microbial cells, for which it can only be speculated as to which of the numerous
enzymes in the cell is actually involved in the transformation.
Table 1.5 Classification of enzymes
Enzyme class
Number
Reaction type
Utility
a
Classified Available
1. Oxidoreductases ~2000
~100
Oxidation/reduction: oxygenation of C–H,
C–C, C¼C bonds, or overall removal or
addition of hydrogen equivalents
+++
2. Transferases
~1900
~100
Transfer of groups: aldehydic, ketonic,
acyl, sugar, phosphoryl, methyl, NH 3
++
3. Hydrolases
~1700
~200
Hydrolysis/formation of esters, amides,
lactones, lactams, epoxides, nitriles,
anhydrides, glycosides, organohalides
+++
4. Lyases
~700
~50
Addition/elimination of small molecules
on C¼C, C¼N, C¼O bonds
++
5. Isomerases
~250
~10
Isomerizations: rearrangement,
epimerization, racemization, cyclization
+
6. Ligases
~200
~10
Formation/cleavage of C–O, C–S, C–N,
C–C bonds with concomitant triphosphate
cleavage
Æ
a
The estimated utility of an enzyme class for the transformation of nonnatural substrates ranges
from +++ (very useful) to Æ (little use) [144]. (Based on the biotransformation database of Kroutil
and Faber (2016) ~17,000 entries.)
1.4 Enzyme Properties and Nomenclature
21