endothelium-derived relaxing factor (EDRF) The
factor originally described as EDRF is NO., produced
by aspecific P-450-type of ENZYMEfrom arginine upon
response of a cell to a biological signal (molecule). Dif-
ferent types of cells respond differently to the presence
of NO..
See alsoCYTOCHROME P-450.
endotherm A warm-blooded animal, one is which
the internal temperature does not fluctuate with tem-
perature of environment, but is maintained by a con-
stant internal temperature regulated by metabolic
processes. Examples include birds and mammals.
endothermic The state of being warm-blooded or
producing heat internally. In chemistry, it is a reaction
where heat enters into a system, with the energy
absorbed by a reactant.
endotoxin A large toxic molecule consisting of
polysaccharide, lipid A, and other components found
in the outer cell wall of specific gram-negative bacteria.
Also called pyrogen or lipopolysaccharide.
energy Classically defined as the capacity for doing
work, energy can occur in many forms such as heat
(thermal), light, movement (mechanical), electrical,
chemical, sound, or radiation. The first law of thermo-
dynamics is often called the Law of Conservation of
Energy and states that energy cannot be created or
destroyed but only transformed from one form into
another.
enhancer Aregulatory element of a gene. A site on
DNA that increases transcription of a region even if it
is distant from the transcribed region. One gene can
have many enhancers.
entatic state Astate of an atom or group that, due
to its binding in a protein, has its geometric or elec-
tronic condition adapted for function. Derived from
the Greek entasis,meaning tension.
enterobactin ASIDEROPHOREfound in enteric bacte-
ria such as Escherichia coli; sometimes called ente-
rochelin.enterochelin SeeENTEROBACTIN.entomology The scientific study of the world of
insects; a branch of zoology.entomophilous Refers to a flower pollinated by
insects.entropy The amount of energy in a closed system
that is not available for doing work; disorder and ran-
domness in a system. The higher the entropy, the less
energy available for work. The Second Law of Thermo-
dynamics states that the entropy of the universe will
always increase.environment The total living and nonliving condi-
tions of an organism’s internal and external surround-
ings that affect an organism’s complete life span.environmental grain Describes an organism’s own
perception of its environment and how it will react to
it; a scale based on the use of space in relation to the
size of an organism. Grains can be coarse (large patch-
es) or fine (small patches).enzootic Affecting animals living in a specific area or
limited region. Slime-blotch disease caused by Brook-
lynella hostilisand its associates caused a Caribbean-
wide mass fish mortality in 1980 and similar ones in
south Florida and Bermuda. In 1990, enzootic pneu-
monia, caused by Mycoplasma hyopneumoniae was
evident in 80 percent of Iowa farms, and on these
farms, 32 percent of the pigs were actively infected.enzyme A macromolecule that functions as a BIO-
CATALYSTby increasing the reaction rate, frequentlyenzyme 115