Glossary of Terms - L

Labile
Unstable or unsteady; not fixed; characterized by adaptability to alteration or modification, i.e., relatively easily changed, as in cleavage of a molecule or molecular rearrangement in a compound or complex chemical material.

LAL (Limulus Amoebocyte Lysate)
A material obtained by rupturing the cellular components of the blood of a horseshoe crab (Limulus Poliphemus). This material coagulates in the presence of LPS (lypopolysaccharides) and is a test used to quantitate bacterial endotoxins (pyrogens).

Laminar Airflow
(also see: Unidirectional Airflow)

Laminar Airflow - Clean Work Station
A workstation in which the unidirectional airflow characteristics predominate throughout the entire airspace with a minimum of eddies (turbulence) to jeopardize critical surfaces.

Laminar Flow
Non-turbulent fluid flow is usually considered laminar if the Reynolds number is less than 2000 in a pipe. Depending upon many possible varying conditions, the flow may be laminar at a Reynolds number as low as 1,200 or as high as 40,000; however, such conditions are not experienced in normal practice. In the pharmaceutical industry, this term incorrectly refers to the air discharge of a clean air bench or wall.

LAN (Local Area Network)
Networks with computers geographically close together (that is, in the same building).

Langelier Index
A measure of the degree of saturation of calcium carbonate in water that is based on pH, alkalinity and hardness. If the Langelier Index is negative, the water is corrosive (pH value below 7 or acidic). If the Langelier Index is positive, calcium carbonate can precipitate out of solution to form scale (pH value above 7 or basic). The Langelier Index will vary for cold water and for warm water.

Latent Heat
The amount of heat needed to change a unit of substance, such as water, from a solid to a liquid without change in temperature or pressure.

Lay
In metallurgy, the direction of the predominant surface pattern ordinarily determined by the production method used.

Leach
To dissolve by the action of a moving liquid. For example, high purity water leaches trace impurities from glass vessels.

Legacy Systems
Hardware and software applications in which a company has already invested considerable time and money. Legacy systems typically perform critical operations in companies for many years even though they may no longer use state-of-the-art technology. Replacing legacy systems can be disruptive and therefore requires careful planning and appropriate migration support from the manufacturer.

LEL (Lower Explosive Limit)


Leptospira
A genus of the family Treponemataceae, thin coiled organisms, flagellated at the extremities, one or both of which are bent back like a hook. Both pathogenic and innocent forms have been isolated.

Leukemia
Cancer that begins in developing blood cells in the bone marrow.

Leukocyte
A general name for white, nucleated blood cells found in the blood and lymphatic tissue.

Level of Product Protection
The level of protection required for an area based on an assessment by the manufacturer of contamination risk.

Ligand
A molecule or ion that is bound to protein.

Ligase
An enzyme used to catalyze the joining of single-stranded DNA segments.

Linkage
The proximity of two or more markers (e.g., genes, RFLP markers) on a chromosome; the closer together the markers are, the lower the probability that they will be separated during DNA repair or replication processes (binary fission in prokaryotes, mitosis or meiosis in eukaryotes), and hence the greater the probability that they will be inherited together.

Linkage Map
A map of the relative positions of genetic loci on a chromosome, determined on the basis of how often the loci are inherited together. Distance is measured in centimorgans (cM).

Lipids
Hydrophobic biological compounds (fats and fatlike materials) that are insoluble in water, but soluble in nonpolar solvents such as benzene, chloroform, and ether. The major components in most lipids are fatty acids.

Lipoprotein
A conjugated protein containing a lipid, prosthetic group.

Liposome
An artificial phospholipid vesicle. Liposomes can be useful for the enclosure of macromolecules such as nucleic acids or, after loading with an appropriate drug. They may be used therapeutically to achieve slow release of the drug into circulation.

Localize
Determination of the original position (locus) of a gene or other marker on a chromosome.

Locus (pl. loci) The position on a chromosome of a gene or other chromosome marker; also, the DNA at that position. The use of locus is sometimes restricted to mean regions of DNA that are expressed.

Long-Range Restriction Mapping
Restriction enzymes are proteins that cut DNA at precise locations. Restriction maps depict the positions on chromosomes of restriction enzyme cutting sites. These are used as biochemical "signposts", or markers of specific areas along the chromosomes. The map will detail the positions on the DNA molecule that are cut by particular restriction enzymes.

Lot


Lot Number


Lou Gehrig's Disease


Lower Flammability Level (LFL)
The minimum concentration of vapor in air at which propagation of flame will occur in the presence of an ignition source. LFL is sometimes referred to as LEL or Lower Explosive Limit.

LPS (Lipopolysaccharide)
Molecule found in the outer cell walls of some bacteria that trigger the immune response resulting in fever. Also referred to as pyrogens or as endotoxins, though, strictly speaking, they are not endotoxins but predominant components of endotoxins produced by gram-negative bacteria. Common cause of pyrogenic reactions in parenteral products.

Lymphocyte
A type of white blood cell accounting for 20-25% of the white cells in humans. They are mostly non-phagocytic and actively mobile and are continuously made in the bone marrow. They are the immediate precursors of all antibody-forming cells.

Lyophilizer
A freeze dryer.

Lyophilization
Also known as freeze drying, it is a means of stabilizing wet substances by freezing them, then evaporating the resulting ice, to leave a substantially dry, porous residue which has the same size and shape of the original frozen mass.

Lysate
A product of lysis, which is the disintegration or dissolution of the cell walls.

Lysine
As essential, basic amino acid obtained from many proteins by hydrolysis.

Lysis
The dissolution or destruction of red blood cells, bacteria, or other antigens by a specific lysin (antibody), or by the action of detergents, thus allowing the cell contents to escape.

Lysosome
A membrane-surrounded organelle in the cytoplasm of eukaryotic cells; it contains many hydrolytic enzymes.