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 and ...
, a lyase is an
enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...
that catalyzes the breaking (an
elimination reaction) of various
chemical bonds 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, elimination, and solvation reactions in which water is the nucleophile.
Biological hydrolysi ...
(a
substitution reaction) and
oxidation
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or ...
, 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
Camp may refer to:
Outdoor accommodation and recreation
* Campsite or campground, a recreational outdoor sleeping and eating site
* a temporary settlement for nomads
* Camp, a term used in New England, Northern Ontario and New Brunswick to descri ...
+ 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
Adenylate cyclase (EC 4.6.1.1, also commonly known as adenyl cyclase and adenylyl cyclase, abbreviated AC) is an enzyme with systematic name ATP diphosphate-lyase (cyclizing; 3′,5′-cyclic-AMP-forming). It catalyzes the following reaction:
:A ...
and
guanylyl cyclase
*
EC 4.99 includes other lyases, such as
ferrochelatase
Membrane-associated lyases
Some lyases associate with
biological membranes as
peripheral membrane protein
Peripheral membrane proteins, or extrinsic membrane proteins, are membrane proteins that adhere only temporarily to the biological membrane with which they are associated. These proteins attach to integral membrane proteins, or penetrate the perip ...
s 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
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