INTRO - A B C D E F G H I J K L M N O P Q R S T U V-Z - INDEX


I

imidazole:
a heterocyclic ring of five atoms (two nitrogens and three carbons) having two double bonds. This ring is part of the side chain of histidine. Certain prooxidant antibiotics are analogues of histidine.

imine (C=N):
any compound possessing a carbon to nitrogen double bond. Imines can be formed by the nucleophilic addition of a primary amine to a carbonyl group followed by the expulsion of water. They can also be formed by the oxidation of a primary or secondary amine when one hydrogen atom is abstracted from the amine nitrogen and another from an adjacent carbon atom. Many imines are unstable in an aqueous environment and readily hydrolyze. Imines which are part of a ring structure tend to be resistent to hydrolysis. Conjugated imines are noted for their ability to redox cycle.

induction:
a physiologic stimulus response function which serves to increase the transcription of a specific locus of DNA to produce mRNA which codes for the increased biosynthesis in the ribosomes of needed proteins. Induction is mediated in many cases by specific transcription factors which are released by some trigger or receptor mechanism. A released transcription factor then migrates to and binds to some specific DNA associated complex where transcription is initiated.

inhibition:
any means (usually chemical) of hindering, slowing, or stopping the function of an enzyme. Some inhibitors permanently deactivate or destroy an enzyme. In such cases the inhibition is considered permanent. Others lessen enzyme activity only temporarily so that the inhibition is considered temporary or reversible. Examples of reversible inhibition include: oxidation of sensitive thiol groups to disulfides, binding of the ligands of the enzyme to a toxic metal, blocking carbonyl groups by imine adduct formation with a toxic amine, exposing a metalloenzyme to another ligand or a chelating agent, blocking the substrate receptor site with a false receptor, increasing product concentration, etc.

inhibitory protein kappa B (I-kappa-B):
a protein subunit of a larger protein complex occurring in the cytoplasm to which nuclear factor kappa B (NF-kappa-B) is loosely bound. Certain physiologic triggers including exposure to oxidants and UV light cause the release of NF-kappa-B from this complex.

initiation:
the first reaction in a sequence of free radical reactions; the event which starts a cascade of repetitive free radical reactions.

initiator:
any substance which can start a free radical chain reaction. Initiators can be reductants or oxidants which tend to react by a single electron transfer, or they can be unstable compounds which readily break up to produce two seperate free radicals. Heat or photons can break covalent bonds and thereby initiate a free radical chain reaction.

iron sulfur center (Fe2S2):
a compound of iron and sulfur which can redox cycle and serve as the active center of certain oxidoreductases. These enzymes have also been called nonheme iron proteins and ferredoxins. They serve as reductants in many anaerobic bacteria. They reduce nitrogen in nitrogen fixing bacteria. They shuttle electrons in photosynthesis and in oxidative phosphorylation.

isocitric acid:
a tricarboxylic acid which is an important component of the Kreb's cycle. It is oxidized/ dehydrogenated by isocitrate dehydrogenase.

isoprene (CH2=CHCH3-CH=CH2):
2-methylbutadiene; a precursor for numerous lipophilic organic compounds. Isoprene units readily polymerize to produce rubbers.

isoprenoids:
organic compounds composed of or containing isoprene units. Examples are: carotenoids, turpenes, rubbers, steroids, tocopherols, ubiquinones, plastoquinone, and phylloquinone.

INTRO - A B C D E F G H I J K L M N O P Q R S T U V-Z - INDEX