Food Biochemistry and Food Processing

6 Enzyme Classification and Nomenclature 137

cause they have a very wide specificity, and it is not
easy to decide if two preparations described by dif-
ferent authors are the same, or if they should be list-
ed under different entries.
While the systematic name always includes “hy-
drolase,” the common name is, in most cases, form-
ed by the name of the substrate with the suffix -ase.
It is understood that the name of this substrate with
the suffix means a hydrolytic enzyme. The peptidas-
es, subclass 3.4, are classified in a different manner
from other enzymes in this class.

Class 4. Lyases

Lyases are enzymes cleaving C–C, C–O, C–N, and
other bonds by means other than hydrolysis or oxi-
dation. They differ from other enzymes in that two
substrates are involved in one reaction direction, but
only one in the other direction. When acting on the
single substrate, a molecule is eliminated, leaving an
unsaturated residue. The systematic name is formed
according to “substrate group-lyase.” In common
names, expressions like decarboxylase, aldolase, and
so on are used. “Dehydratase” is used for those en-
zymes eliminating water. In cases where the reverse
reaction is the more important, or the only one to be
demonstrated, “synthase” may be used in the name.

Class 5. Isomerase

These enzymes catalyze changes within one mole-
cule.

Class 6. Ligases

Ligases are enzymes catalyzing the joining of two
molecules with concomitant hydrolysis of the di-
phosphate bond in ATP or a similar triphosphate.
The bonds formed are often high-energy bonds.
“Ligase” is commonly used for the common name,
but in a few cases, “synthase” or “carboxylase” is
used. Use of the term “synthetase” is discouraged.

GENERALRULES ANDGUIDELINES FOR
CLASSIFICATION ANDNOMENCLATURE OF
ENZYMES

Table 6.1 shows the classification of enzymes by
class, subclass, and sub-subclass, as suggested by

the Nomenclature Committee of the International

Union of Biochemistry and Molecular Biology (NC-

IUBMB). The information is reformatted in table

form instead of text form for easier reading and

comparison.

Table 6.2 shows the rules for systematic names

and guidelines for common names as suggested by

NC-IUBMB. Table 6.3 shows the rules and guide-

lines for particular classes of enzymes as suggested

by NC-IUBMB. The concept on reformatting used

in Table 6.1 is also applied.

EXAMPLES OF COMMON FOOD

ENZYMES

The food industry likes to use terms more easily

understood by its people and is slow to adopt

changes. For example, some commonly used terms

related to enzymes are very general terms and do not

follow the recommended guidelines established by

NC-IUBMB. Table 6.4 is a list of enzyme groups

commonly used by the food industry and

researchers (Nagodawithana and Reed 1993).

Table 6.5 lists some common names, systematic

names, and EC numbers for some common food en-

zymes.

Enzyme classification and nomenclature are now

standardized procedures. Some journals already

require that enzyme codes be used in citing or nam-

ing enzymes. Other journals are following the trend.

It is expected that all enzymes will have enzyme

codes in new research articles as well as (one hopes)

in new reference books. However, for older litera-

ture, it is still difficult to identify the enzyme codes.

It is hoped that Tables 6.4 and 6.5 will be useful as

references.

ACKNOWLEDGMENT

The authors thank the International Union of

Biology and Molecular Biology for permission to

use of some of the copyrighted information on En-

zyme Classification and Nomenclature. The authors

also want to thank Prof. Keith Tipton, Department of

Biochemistry, Trinity College, Dublin 2, Ireland, for

his critical review of this manuscript.