catabolic pathway The process for taking large
complex organic molecules and breaking them down
into smaller ones, which release energy that can be
used for metabolic processes.
catabolism Reactions involving the breaking down
of organic SUBSTRATEs, typically by oxidative break-
down, to provide chemically available energy (e.g., ATP)
or to generate metabolic intermediates used in subse-
quent anabolic reactions.
See alsoANABOLISM; METABOLISM.
catabolite A naturally occurring METABOLITE.
catabolite activator protein (CAP) A protein that
binds cyclic adenosine monophosphate (cAMP), a regu-
latory molecule, to DNA in organisms. When this inter-
action takes place, the gene promoter is made
accessible to the enzyme RNA polymerase, and tran-
scription of the gene can begin.
catalase A HEMEprotein that catalyzes the DISPRO-
PORTIONATIONof dihydrogen peroxide to O 2 and water.
It also catalyzes the oxidation of other compounds,
such as ethanol, by dihydrogen peroxide. A nonheme
protein containing a dinuclear manganese CLUSTERwith
catalase activity is often called pseudocatalase.
catalysis The action of a CATALYST.
catalysis law SeeBRONSTED RELATION.
catalyst A substance that participates in a particular
CHEMICAL REACTIONand thereby increases its rate, but
without a net change in the amount of that substance
in the system. At the molecular level, the catalyst is
used and regenerated during each set of MICROSCOPIC
CHEMICAL EVENTs leading from a MOLECULAR ENTITY
of reactant to a molecular entity of product.
See alsoAUTOCATALYTIC REACTION; BIFUNCTIONAL
CATALYSIS; CATALYTIC COEFFICIENT; ELECTRON-TRANS-
FER CATALYSIS; GENERAL ACID CATALYSIS; GENERAL BASE
CATALYSIS; HOMOGENEOUS CATALYST; HETEROGENEOUS
CATALYST; INTRAMOLECULAR CATALYSIS; MICELLAR
CATALYSIS; MICHAELIS-MENTEN KINETICS; PHASE-
TRANSFER CATALYSIS; PSEUDOCATALYSIS; RATE OF REAC-
TION; SPECIFIC CATALYSIS.catalytic antibody(abzyme) An ANTIBODYthat cat-
alyzes a chemical reaction analogous to an enzymatic
reaction, such as an ester hydrolysis. It is obtained by
using a hapten that mimics the transition state of the
reaction.
See alsoENZYME.catalytic coefficient If the RATE OF REACTION(v)is
expressible in the form
v= (k 0 + Σki[Ci]n;i) [A]α[B]β...
where A, B, ... are reactants and Cirepresents one of a
set of catalysts, then the proportionality factor kiis the
catalytic coefficient of the particular CATALYSTCi. Nor-
mally, the partial order of reaction (ni) with respect to a
catalyst will be unity, so that kiis an (α+ β+...+1)th-
order rate coefficient. The proportionality factor k 0 is
the (α+ β+ ...)th-order rate coefficient of the uncat-
alyzed component of the total reaction.catenation The tendency of an element to form
bonds to itself into chains or rings.cathode The negative part of an electric field; elec-
trode where reduction occurs.cathode-ray tube Closed glass tube containing a gas
under low pressure; produces cathode rays (electrons)
when high voltage is applied.cathodic protection Protection of a metal against
corrosion by making it the cathodic part of an electro-
chemical cell in which the anode is a more easily oxi-
dized metal.cation A positively charged ION.42 catabolic pathway