EC nomenclature for enzymes A classification of
ENZYMEs according to the Enzyme Commission of the
International Union of Biochemistry and Molecular
Biology. Enzymes are allocated four numbers, the first
of which defines the type of reaction catalyzed; the next
two define the SUBSTRATEs, and the fourth is a catalogue
number. Categories of enzymes are EC 1, OXIDOREDUC-
TASEs; EC 2, TRANSFERASEs; EC 3, HYDROLASEs; EC 4,
LYA S Es; EC 5, ISOMERASEs; EC 6, LIGASEs (Synthetases).
ecosystem Any natural system including biotic and
abiotic parts that interact as a unit to produce a sta-
ble functioning system through cyclical exchange of
materials.
EDRF SeeENDOTHELIUM-DERIVED RELAXING FACTOR.
educt Used mainly in the German literature as a term
for starting material (reactant). It should be avoided in
English because in that context it means “something
that comes out” and not “something that goes in.” The
German use of the term is in fact also incorrect.
effective atomic number Represents the total num-
ber of electrons surrounding the nucleus of a metal
atom in a metal complex, and is calculated from the
composition and atomic numbers of a compound or
mixture. In the organometallic chemistry of transition
metals, the metal atom often forms bonds such that all
of the valence shell orbitals are filled, so that the total
number of electrons in its valence shell is 18, which is
effectively the configuration of the next noble gas. Also
called the 18-electron rule. The term is used in different
contexts to represent an effective average atomic num-
ber of a multicomponent system.effective charge Change in effective charge is a
quantity obtained by comparison of the POLAR EFFECT
of substituents on the free energies of rate or equilib-
rium processes with that on a standard ionization equi-
librium. Provided that the effective charge on the states
in the standard equilibrium is defined, it is possible to
measure effective charges for states in the reaction or
equilibrium under consideration.effective collisions A collision between two mole-
cules or reactants that results in a reaction or that pro-
duces a product, and where the colliding particles have
the necessary amount of energy and orientation to pro-
duce the reaction.effective molarity(effective concentration) The ratio
of the first-order rate constant of an INTRAMOLECULAR
reaction involving two functional groups within the same
MOLECULAR ENTITYto the second-order RATE CONSTANT87