In
biochemistry
Biochemistry, or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology, a ...
, a lyase is an
enzyme
An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...
that catalyzes the
breaking (an
elimination reaction) of various
chemical bond
A chemical bond is the association of atoms or ions to form molecules, crystals, and other structures. The bond may result from the electrostatic force between oppositely charged ions as in ionic bonds or through the sharing of electrons a ...
s by means other than
hydrolysis
Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...
(a
substitution reaction) and
oxidation
Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...
, often forming a new
double bond or a new
ring structure. The reverse reaction is also possible (called a
Michael reaction). For example, an enzyme that catalyzed this reaction would be a lyase:
:
ATP →
cAMP + PP
i
Lyases differ from other enzymes in that they require only one
substrate for the reaction in one direction, but two substrates for the reverse reaction.
Nomenclature
Systematic names are formed as "''substrate group-lyase''." Common names include
decarboxylase,
dehydratase,
aldolase, etc. When the product is more important,
synthase may be used in the name, e.g. phosphosulfolactate synthase (EC 4.4.1.19, Michael addition of sulfite to phosphoenolpyruvate).
A combination of both an elimination and a Michael addition is seen in O-succinylhomoserine (thiol)-lyase (MetY or MetZ) which catalyses first the γ-elimination of O-succinylhomoserine (with succinate as a leaving group) and then the addition of sulfide to the vinyl intermediate, this reaction was first classified as a lyase (EC 4.2.99.9), but was then reclassified as a transferase (EC 2.5.1.48).
Classification
Lyases are classified as EC 4 in the
EC number classification of enzymes. Lyases can be further classified into seven subclasses:
*
EC 4.1 includes lyases that cleave carbon–carbon bonds, such as
decarboxylases (EC 4.1.1),
aldehyde lyases (EC 4.1.2), oxo acid lyases (EC 4.1.3), and others (EC 4.1.99)
*
EC 4.2 includes lyases that cleave carbon–oxygen bonds, such as
dehydratases
*
EC 4.3 includes lyases that cleave carbon–nitrogen bonds
*
EC 4.4 includes lyases that cleave carbon–sulfur bonds
*
EC 4.5 includes lyases that cleave carbon–halide bonds
*
EC 4.6 includes lyases that cleave phosphorus–oxygen bonds, such as
adenylyl cyclase and
guanylyl cyclase
*
EC 4.99 includes other lyases, such as
ferrochelatase
Membrane-associated lyases
Some lyases associate with
biological membranes as
peripheral membrane proteins or anchored through a single
transmembrane helix.
Superfamilies of single-pass transmembrane lyases
in Membranome database
See also
* List of EC numbers of enzymes belonging to category EC 4
References
EC 4 Introduction
from the Department of Chemistry at Queen Mary, University of London
{{enzyme-stub