phagocytic cells have receptors enabling them to take up antigen-antibody complexes for subsequent destruction by the phagocytic cell. This route is also a means exploited by certain viruses and toxins to gain entry into cells through the otherwise impervious cell membranes (e.g., used by the AIDS virus and the Semliki Forest Virus). Disorders of endocytosis can lead to disease states (e.g., high cholesterol levels in the blood of people whose low-density lipoprotein receptors are impaired). Drugs (e.g., certain painkillers) can be targeted to specific receptors via receptor mapping (RM) and receptor fitting (RF) for greater efficacy. See also INVASIN,

ADHESION MOLECULE, CD4 PROTEIN, EXOCYTOSIS,

T CELL RECEPTORS, SIGNAL TRANSDUCTION, VAG-

INOSIS, RECEPTORS, RECEPTOR FITTING (RF),

HIGH-DENSITY LIPOPROTEINS (HDLPs), LOW-DEN-

SITY LIPOPROTEINS (LDLPs), RECEPTOR MAPPING

(RM), SIGNALING, NUCLEAR RECEPTORS.

Endodermal Adult Stem Cells Certain stem cells present within (adult) bodies of organisms, that can be differentiated (via chemical signals) to give rise to cells of tongue, tonsils, the bladder/urethra, digestive tract, liver, pancreas, lung tissues, etc. See also STEM

CELLS, MULTIPOTENT ADULT STEM CELLS, CELL,

ORGANISM, SIGNALING.

Endoglycosidase An enzyme capable of hydrolyzing (breaking) interior bonds in the oligosaccharide molecular branches of a glycoprotein molecule. That is, the enzyme is capable of cutting a sugar-to-sugar bond anywhere within the sugar polymer molecule (depending, of course, on the specificity of the enzyme). This is in contrast to an exoglycosidase, which must cut away at the polymer from the outside, i.e., from the free end, one unit (or section, as the case may be) at a time. See also EXOGLYCOSIDASE,

GLYCOPROTEIN, ENZYME, OLIGOSACCHARIDES,

RESTRICTION ENDOGLYCOSIDASES, HYDROXYLA-

TION REACTION.

Endometrium The lining of the uterus. Endonucleases A class of enzymes capable of

hydrolyzing (breaking) the interior phosphodiester bonds of DNA or RNA chains. As opposed to cleavage (by exonucleases) at the terminal bonds (ends) of a chain. See

also ENZYME, DNase 1, DNase 2, EXONUCLEASE,

ENDOGLYCOSIDASE.

Endophyte A microrganism (fungus or bacterium) that lives inside vascular tissues of plants (in spaces between plant cells). At least one company has incorporated the gene for a protein toxic to insects (taken from Bacillus thuringiensis) into an endophyte to confer insect resistance to a crop plant. When endo-

phyte-infested fescue grass is fed to cattle, E sheep, horses, or rabbits, it is generally toxic

to those animals, due to mycotoxin(s) or alkaloids produced by that endophyte. See also

MICROORGANISM, BACTERIA, BACILLUS THURING-

IENSIS (B.t.), FUNGUS, PROTEIN, MYCOTOXINS,

TREMORGENIC INDOLE ALKALOIDS.

Endoplasmic Reticulum (ER) A highly specialized, complex network of branching, intercommunicating tubules (surrounded by membranes) found in the cytoplasm of most animal and plant cells. The two types of ER recognized are: rough ER and smooth ER. Rough ER is covered with many ribosomes; ER without or with fewer ribosomes attached is called smooth. This nomenclature comes about because of the appearance of the ER under high magnification. The rough ER is very well developed to facilitate cells carrying on abundant protein synthesis, because proteins are synthesized (manufactured) in ribosomes. See also CELL, CYTOPLASM,

RIBOSOMES, FATS, LIPIDS, PLASMA MEMBRANE,

PROTEIN, PHOSPHOLIPIDS.

Endorphins Discovered during the 1970s by U.S. and Scottish scientists, these hormones are produced in the brain, and act as natural painkillers. For example, runners and longdistance walkers achieve something of a “high” due to endorphins released during long runs or walks. See also ENKEPHALINS,

CATECHOLAMINES, HORMONE.

Endosome See ENDOCYTOSIS.

Endosperm The interior portion of a plant seed, beneath the outer hull (the portion that people tend to eat, in food crops). In grains (e.g., rice or corn/maize), the endosperm consists primarily of starch (carbohydrate). In legumes (e.g., beans), the endosperm contains mainly protein, a small amount of carbohydrates, and sometimes vegetable oil.

See also STARCH, CORN, SOYBEAN PLANT,

CARBOHYDRATES (SACCHARIDES), SOYBEAN OIL,

ALEURONE.

Endospore A highly resistant, dormant inclusion body formed within certain bacteria. To kill spores, temperatures above boiling are usually needed. For this, pressure cookers and autoclaves are required. Endospores have survival value since the spore can remain for

Eand then, under appropriate conditions, can be induced to germinate and regenerate the original cell. Endospore formation may be

viewed as being akin to hibernation, i.e., a kind of “bacterial hibernation.”long periods of time in a nongrowing state

Endostatin An antiangiogenesis human protein discovered by Judah Folkman. In concert with angiostatin, it causes certain cancer tumors in mice to shrink. See also PROTEIN,

ANTIANGIOGENESIS, ANGIOSTATIN, CANCER.

Endothelial Cells These are the flat, sort of plate-shaped cells that line the surface of all blood vessels, heart, and lymphatics within the body. Endothelial cells possess transmembrane (through the cell membrane) molecules known as adhesion molecules, which selectively allow the passage (from bloodstream to tissues) of some molecules (leukocytes, monocytes, hormones, etc.). Endothelial cells are packed much tighter together in the capillaries that provide blood to the brain. This tighter packing limits the size and kind of molecules that can pass into the brain. This blood-brain barrier serves to protect the sensitive brain tissue from pathogens or harmful molecules (e.g., toxins). See

also ENDOTHELIUM, VASCULAR ENDOTHELIAL

GROWTH FACTOR (VEGF), ADHESION MOLECULES,

MONOCYTES, MITOGEN, SELECTINS, BLOOD-BRAIN

BARRIER (BBB), LECTINS, ELAM-1, ATP SYNTHASE,

OXIDATIVE STRESS, CYCLOOXYGENASE.

Endothelin A peptide that causes arteries to contract (which consequently causes blood pressure to increase). See also PEPTIDE,

ATRIAL PEPTIDES.

Endothelium The layer of epithelial cells that line blood vessels throughout the body. The layer selectively allows the passage (from bloodstream to tissues) of nutrients, hormones, and other molecules essential for tissue growth and function. The endothelium is involved in the recovery and recycling of

old red blood cells. It also produces nitric oxide, which causes neighboring smoothmuscle (blood vessel) cells to relax so that those (neighboring ) blood vessels dilate and the body’s blood pressure is lowered, and two compounds, prostacyclin and Von Willebrand factor, that prevent blood clotting. See also

ENDOTHELIAL CELLS, VASCULAR ENDOTHELIAL

GROWTH FACTOR (VEGF), SELECTINS, LECTINS,

ADHESION MOLECULES, NITRIC OXIDE, NITRIC

OXIDE SYNTHASE, BILIRUBIN.

Endotoxin A lipopolysaccharide (fat/sugar complex; poison, also known as LPS) which forms an integral part of the cell wall of gram negative bacteria. It is only released when the cell is ruptured. It can cause, among other things, septic shock and tissue damage. Pharmaceutical preparations are routinely tested for the presence of endotoxins. This is one reason why pharmaceuticals must be prepared in a sterile environment. See also

SEPSIS, BACTERIA, LIPIDS, POLYSACCHARIDES,

TOXIN, CHOLERA TOXIN, GRAM-NEGATIVE (G- ),

GOOD MANUFACTURING PRACTICES (GMP).

Engineered Antibodies Chimeric monoclonal antibodies, produced via genetic engineering of human antibody-producing cells (clones). For example, the genes coding for antilymphoma binding sites from a rat have been inserted into human antibody-producing cells to yield rat (antigen) binding sites mounted on human antibody “stems." See

also CHIMERIC PROTEINS, MONOCLONAL ANTI-

BODIES (MAb), ANTIBODY, GENETIC ENGINEERING,

COMBINING SITE, LYMPHOCYTE, SEMISYNTHETIC

CATALYTIC ANTIBODY.

Enhanced Nutrition Crops See

ENHANCED™.

Enkephalins A class of hormones produced in the brain that act as natural painkillers. Discovered by John Hughes and Hans Kosterlitz in 1975, they are some of the endorphins.

See also ENDORPHINS.

Enolpiruvil Shikimate See EPSP SYNTHASE. Enolpyruvil Shikimate See EPSP SYNTHASE. Enoyl-acyl Protein Reductase A n e n z y m e

that is utilized by bacteria in their synthesis (manufacture) of fatty acids. See also ENZYME,

PROTEIN, BACTERIA, FATTY ACID, ESSENTIAL

FATTY ACIDS.

Ensiling The fermentation of (usually chopped up) agricultural vegetation in order to preserve it. It is carried out for 1–2 weeks, using either indigenous microorganisms (e.g., Lactobacillus spp.) or introduced microorganisms (to speed up the process, yield product containing more nutrients for livestock, etc.), in the absence of oxygen (to prevent the growth of aerobic mold fungi). When indigenous microorganisms are used, Lactobacillus spp. become the dominant microorganisms present, and heat is generated by the microorganisms within the vegetative mass (optimum temperature is 25–30°C, which is 77–86°F). Lactic acid produced by the microorganisms inhibits the growth of bacteria that would normally putrefy the veg-

etation. See also FERMENTATION, MICROORGANISM, AEROBIC, FUNGUS, OPTIMUM TEMPERATURE.

Enterohemorrhagic E. coli The several dozen (approximately 60 known) serotypes (strains) of E. coli bacteria that cause internal hemorrhaging in humans that ingest those bacteria. The toxin produced by these particular E. coli bacteria attacks the human kidney, which often leads to kidney failure and/or death. See also ESCHERICHIA COLIFORM

0157:H7 (E. COLI 0157:H7), TOXIN, SEROTYPES,

ENTEROTOXIN.

Enterotoxin The category (i.e., intestinally active) of toxins, produced by certain bacterial strains and/or serotypes, which attack the body’s internal organs. For example, the serotype of Escherichia coliform bacteria known as E. coli 0157:H7 attacks the kidneys and other internal organs of humans, also causing internal bleeding and sometimes death. See also TOXIN, BACTERIA,

E S C H E R I C H I A C O L I F O R M 0 1 5 7 :H 7 , E N T E R -

PHEMORHAGIC E. COLI, SEROTYPES, CHOLERA

TOXIN.

Enzyme An organic, protein-based catalyst that is not itself used up in the reaction. It is naturally produced by living cells to catalyze biochemical reactions. Each enzyme is highly specific with regard to the type of chemical reaction that it catalyzes, and to the substances (called substrates) upon which it acts. This specific catalytic activity and its control by other biochemical constituents are of primary importance in the physiological

functions of all organisms. Although all enzymes are proteins, they may, and usually do, contain additional nonprotein components called coenzymes that are essential for catalytic activity. See also APOENZYME, CATA-

stops the synthesis of mRNA, and therefore the synthesis of the protein is also blocked.

See also ENZYME, REPRESSION (OF AN ENZYME),

ENZYME DEPRESSION.

Enzyme-Linked Immunosorbent Assay See

ELISA.

Eosinophils Polymorphonuclear leukocytes made in the bone marrow. They circulate in

Eeight) and then migrate into the tissue where they reside. They kill parasites too large to be phagocytized by secreting substances that kill the parasites (hookworms, trichinosis, etc.), inhibit histamine release from mast cells, and secrete chemicals that neutralize

histamine. Allergy causes an increase in eosinophils. GM-CSF stimulates eosinophilthe blood for a number of hours (three to

production. See also POLYMORPHONUCLEAR

LEUKOCYTES (PMN), BASOPHILS, ANTIGEN,

CELLULAR IMMUNE RESPONSE.

EPD See EXPECTED PROGENY DIFFERENCES.

Epidermal Growth Factor (EGF) A protein of 53 amino acids that greatly increases growth/reproduction of epidermal (skin) cells. This protein also increases growth of wool in sheep and growth in more than 50% of human tumors. High concentrations of epidermal growth factor are found in human tears. EGF was discovered by Stanley

Cohen. See also PROTEIN, EGF RECEPTOR,

GROWTH FACTOR, NERVE GROWTH FACTOR (NGF),

AMINO ACID, FILLER EPITHELIAL CELLS, TUMOR.

Epidermal Growth Factor Receptor See EGF

RECEPTOR, HER-2 RECEPTOR, HER-2 GENE.

Epimerase An enzyme capable of the reversible interconversion of two epimers. See also

ENZYME, EPIMERS.

Epimers Two stereoisomers differing in con-

figuration. See also CONFIGURATION, STEREOISOMERS.

Episome (of a bacterium) An independent genetic element (DNA) that occurs inside bacterium in addition to the normal bacterial cell genome. The episome can replicate either as an autonomous unit or as one integrated into the host genome. The F (fertility) factor is an episome. See also GENOME, PLASMID,

BACTERIA, DEOXYRIBONUCLEIC ACID (DNA).

Epistasis Interaction between nonallelic genes in which the presence of a certain allele at one locus prevents expression of an allele at

a different locus. See also ALLELE, GENE,

EXPRESS, LOCUS.

Epithelial Projections Projections that anchor the epidermis (surface skin) to the dermis (subsurface tissue). Growth of these projections is increased by epidermal growth factor during the wound healing process. See also

EPIDERMAL GROWTH FACTOR (EGF).

Epithelium The prefix epi- means on, above, or upon. The membranous cellular tissue that covers a free surface or lines a tube or cavity of an animal body. It serves to enclose and protect the other tissues, to produce secretions and excretions, and to function in assimila-

tion. See also ASSIMILATION, CADHERINS, ION

CHANNELS.

Epitope Also called antigenic determinant. The specific group of atoms (on an antigen molecule) that is recognized by (that antigen’s) antibodies (thereby causing an immune

response). See also ANTIBODY, ANTIGEN, IDIOTYPE, HUMORAL IMMUNE RESPONSE.

EPO See ERYTHROPOIETIN, EUROPEAN PATENT

OFFICE.

EPPO See EUROPEAN PLANT PROTECTION ORGANI-

ZATION.

EPSP Synthase Enolpyruvyl-shikimate phosphate synthase. An enzyme produced by virtually all plants and internally transported into their cells’ chloroplasts, it is essential in a plant’s metabolism biochemical pathway and for the biosynthesis (creation) of the aromatic (ring-shaped molecule) amino acids tyrosine, phenylalanine, and tryptophan, which are needed for plants to live. Some (glyphosate-containing and sulfosatecontaining) herbicides kill unwanted plants (e.g., weeds) by inhibiting EPSP synthase. By incorporating a gene that causes (over-) production of CP4 EPSP synthase into several crops (soybeans, cotton, etc.), scientists have been able to help those crops survive post-emergence application(s) of glypho- sate-containing herbicide. Additional resistance to glyphosate - containing and sulfosate-containing herbicides can be conferred to plants by incorporating into plants a gene (GO) which causes those plants to produce glyphosate oxidase. See also

ENZYME, METABOLISM, GENE, PAT GENE, BAR

GENE, GENETIC ENGINEERING, SOYBEAN PLANT,