laccase:
a copper (Cu) containing oxidase present in many plants
which converts polyphenols into orthoquinones. Laccase
is activated upon injury to plant tissue. lactic acid (CH3-HCOH-COOH):
beta-hydroxy-n-propanoic acid; the product of hydrogenation
of pyruvic acid. Lactic acid tends to be produced under
anaerobic conditions when other oxidants are not available to
take up reducing equivalents produced by glycolysis. Lactic acid
levels are often elevated in fatigued states.
lactic acidosis:
the accumulation of large quantities of lactic acid under
conditions of increased demand for ATP and deficiency of
oxygenation. Localized lactic acidosis accounts for the burning
sensation within heavily worked muscles. Systemic lactic
acidosis occurs in shock and other conditions of serious oxygen
deprivation.
lactoferrin:
a protein which can readily bind iron cations; a naturally
occurring chelator of iron. The sequestration of excess iron has been
found to induce antiinfective and antitumor benefits and to lessen the
spontaneous generation of oxyradicals.
lag phase:
the segment of time after bacteria have been innoculated into
nutrient growth media before they begin to divide. The lag phase has been
shown to correspong with the build up of reducing conditions in the media
which must occur or else growth is inhibited.
lapachol:
2-hydroxy-3-(3,3-dimethylallyl)-1,4,-naphthoquinone; a quinone naturally
occuring in the bark and wood of Tabebuia avellanedae
(pao d' arco, ipe roxo, lapacho), in Tecoma araliaceae,
and in other species of Bignoniaceae. A related compound is beta-lapachone.
These quinones have demonstrated immunostimulating, antiinfective, and antineoplastic effects.
lawsone:
2-hydroxy-1,4-naphthoquinone; a naphthoquinone naturally occuring
in the leaves of henna (the Egyptian privet, Lawsonia inermis, L. alba).
Henna has been used since ancient times as a cosmetic red dye. Henna is a
medicinal herb in Africa, Middle East, and India.
leukotriene:
a docosoid with long acting proinflammatory effects. Reduced
glutathione is required as a precursor in the synthesis of some
leukotrienes.
leukoflavin (FADH2):
dihydroflavin; the fully reduced form of flavin. FADH2
is colorless due to loss of the extended conjugation of double bonds
found in its oxidized yellow colored counterpart FAD.
ligand:
a molecule having alkaline, electrophilic, negatively charged, or
dipolar reactive groups, which bind to metallic cations. Chelating agents
are composed of two or more ligands.
liothyronine (T3):
an aromatic hormone produced in vivo by the deiodinization
of thyroxin (T4). T3 is the more active of the two thyroid hormones.
Both T4 and T3 induce enhanced activity of glycerol-3-phosphate
dehydrogenase which removes excessive reductants from the cytoplasm for
oxidation in the mitochondria.
lipid peroxidation:
the chemical process by which lipids react with diatomic
oxygen to produce lipid peroxides. The key steps involve abstraction of
hydrogen from a sensitive lipid to form a carbon centered free radical
(L*). Next diatomic oxygen adds itself to L* producing an alkylperoxyl
radical (LOO*). Reduction of this species results in the production of
the lipid hydroperoxide (LOOH). If LOO* can succeed in abstracting
hydrogen from still other lipids, then the reaction will self propagate.
lipid peroxide (LOOH):
an organic hydroperoxide of naturally occurring oils.
lipoamide:
the carboxylic end of lipoic/thioctic acid condensed as an amide bond
with the amino group on the side chain of lysine within an enzyme.
This structure permits cyclic movement of the redox active end
of the lipoic/thioctic acid within the enzyme. Such enzymes serve
to dehydrogenate and decarboxylate alpha-keto-carboxylic acids.
lipoic acid:
thioctic acid; an eight carbon carboxylic acid with thiol
groups at the 6th and 8th positions. This molecule can redox cycle
as it switches between a dithiol and a disulfide form. It enzymatically
produces transferable hydrogen atoms and can therefore serve as an
important metabolic source of reductants. It can also shuttle hydrogen
atoms within and among cells. It is an important reductive antioxidant.
Since thiol groups can also function as ligands, lipoic acid can chelate
cationic metals including mercury II (Hg++).
lipophil / lipophilic compound:
any molecule which is soluble in lipid media. Most lipophiles are
weakly soluble or insoluble in aqueous media.
logarithmic phase:
the period of rapid growth of an organism in media during
which mitosis is actively occuring and the numbers continue doubling.
The logarithmic phase cannot commence until the medium reaches a reductive
potential.
lysyl oxidase:
an enzyme which oxidatively deaminates the primary amine of
the lysine residue of certain proteins. This converts it to an aldehyde
which is further metabolized to form crosslinks which strengthen the
protein. Lysyl oxidase utilizes copper as part of its redox active center.
