of an analogous INTERMOLECULARelementary reaction.
This ratio has the dimension of concentration. The term
can also apply to an equilibrium constant.
See alsoINTRAMOLECULAR CATALYSIS.
effective nuclear charge That portion of the nuclear
charge that is experienced by the highest-energy-level
electrons (outermost electrons) in an atom.
efficacy Describes the relative intensity with which
AGONISTs vary in the response they produce, even when
they occupy the same number of RECEPTORs with the
same AFFINITY. Efficacy is not synonymous with
INTRINSIC ACTIVITY.
Efficacy is the property that enables DRUGs to pro-
duce responses. It is convenient to differentiate the
properties of drugs into two groups: those that cause
them to associate with the receptors (affinity) and those
that produce stimulus (efficacy). This term is often used
to characterize the level of maximal responses induced
by agonists. In fact, not all agonists of a receptor are
capable of inducing identical levels of maximal
responses. Maximal response depends on the efficiency
of receptor coupling, i.e., from the cascade of events
that, from the binding of the drug to the receptor, leads
to the observed biological effect.
effusion The flow of gases through small openings in
comparison with the distance between molecules.
EF-hand A common structure to bind Ca2+ in
CALMODULINand other Ca2+-binding proteins consist-
ing of a HELIX(E), a loop, and another helix (F).
See alsoMETABOLIC REGULATION.
eighteen-electron rule An electron-counting rule to
which an overwhelming majority of stable diamagnetic
transition metal complexes adhere. The number of non-
bonded electrons at the metal plus the number of elec-
trons in the metal-ligand bonds should be 18. The
18-electron rule in transition metal chemistry is a full
analog of the Lewis octet rule, also known as the effec-
tive atomic number rule.
Eijkman, Christiaan(1858–1930) NordicPhysician
Christiaan Eijkman was born on August 11, 1858, at
Nijkerk in Gelderland (the Netherlands) to Christiaan
Eijkman, the headmaster of a local school, and
Johanna Alida Pool. He received his education at his
father’s school in Zaandam. In 1875 he entered the
Military Medical School of the University of Amster-
dam and received training as a medical officer for the
Netherlands Indies Army. From 1879 to 1881 he wrote
his thesis “On Polarization of the Nerves,” which
gained him his doctor’s degree, with honors, on July
13, 1883. On a trip to the Indies he caught malaria and
returned to Europe in 1885.
Eijkman was director of the Geneeskundig Labora-
torium (medical laboratory) in Batavia from 1888 to
1896, and during that time he made a number of
important discoveries in nutritional science. In 1893 he
discovered that the cause of beriberi was the deficiency
of vitamins, not of bacterial origin as thought by the
scientific community. He discovered vitamin B, and this
discovery led to the whole concept of vitamins. For this
discovery he was given the Nobel Prize in physiology
or medicine for 1929.
He wrote two textbooks for his students at the
Java Medical School, one on physiology and the other
on organic chemistry. In 1898 he became professor in
hygiene and forensic medicine at Utrecht, but also
engaged in problems of water supply, housing, school
hygiene, physical education, and, as a member of the
Gezondheidsraad (health council) and the Gezond-
heids commissie (health commission), he participated
in the struggle against alcoholism and tuberculosis. He
was the founder of the Vereeniging tot Bestrijding van
de Tuberculose (Society for the Struggle against Tuber-
culosis). Eijkman died in Utrecht on November 5,
1930.
Eijkman’s syndrome, a complex of nervous symp-
toms in animals deprived of vitamin B1, is named for
him.Einthoven, Willem(1860–1927) NordicPhysiolo-
gist Willem Einthoven was born on May 21, 1860, in
Semarang on the island of Java, Indonesia, to Jacob
Einthoven, an army medical officer in the Indies, and
Louise M.M.C. de Vogel, daughter of the director of
finance in the Indies.88 effective nuclear charge