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


G

gallic acid:
a polyphenolic organic acid found in many plants usually bound to some organic alcohol such as a glycoside or a bioflavonoid forming an ester. The structure of gallic acid resembles benzoic acid with three hydroxyl groups bound to the aromatic ring at the opposite side of the carboxyl group. Due to their phenolic structure, gallates are effective oxyradical quenchers. Upon oxidation gallates become bitter tasting and astringent orthoquinones.

glucose-6-phosphate (G6P):
an ester of phosphoric acid with the hydroxyl group at carbon 6 of glucose; a metabolically activated form of glucose produced by enzymatic phosphorylation from ATP. This is the first step in the utilization of glucose in anaerobic glycolysis and in the hexose monophosphate shunt.

glucose-6-phosphate dehydrogenase (G6PDH):
an enzyme which reduces NADP+ using hydrogen abstracted from G6P; the first step in the hexose monophosphate shunt which produces large quantities of NADPH.

glutamic acid (glu):
an amino acid which has a side chain composed of three methylene groups with a terminal carboxyl group.

glutaredoxin (Grx):
an enzyme possessing two redox active cysteine residues which can activate ribonucleoside reductase (RR). Grx can accept hydrogen atoms from glutathione (GSH) or from protein disulfide isomerase (PDI) and subsequently transfer them to RR.

glutathione (GSH):
gamma-glutamyl-cysteinyl-glycine; a ubiquitous tripeptide with a redox active thiol group. GSH has numerous roles as a physiologic hydrogen carrier and antioxidant. Many thiol compounds including certain enzymes, cofactors, and transcription factors are maintained in the reduced state by the hydrogen donating function of GSH. An important selenium containing peroxidase depends on GSH for activation.

glutathione disulfide (GSSG):
a dimer of glutathione produced by oxidative coupling of GSH. Upon donation of its hydrogen atom to an oxidant, GSH becomes the glutathyil radical (GS*). Two of these couple to become GSSG. GSSG can accept hydrogen from numerous donors thus behaving as a weak oxidant. GSSG also participates in thiol-disulfide exchange reactions. Intracellular GSSG triggers the release of NF-kappa-B in certain cells.

glutathione peroxidase (GP):
glutathione:peroxide oxidoreductase; an enzyme which oxidizes glutathione and reduces peroxides. GP picks up hydrogen atoms from GSH and passes them on to hydrogen peroxide or to lipid peroxide(s) producing water and / or alcohols. GP utilizes the amino acid selenocysteine in its redox active center.

glutathione reductase (GR):
NADPH:glutatione disulfide oxidoreductase; a flavoprotein (utilizing FAD) which transfers electrons from NADPH to GSSG producing NADP+ and GSH. GR maintains most of the glutathione of the cytosol in the reduced state. GR activity is increased whenever oxidants deplete hydrogen atoms from the GSH pool. The production of more GP is induced in response to stimulation by most oxidants including oxyradicals. When GR activity is high much NADPH is converted to NADP+, thus less reducing equivalents are available for other functiuons such as syntheses.

glutathione-S-transferase (GST):
a conjugase which covalently attaches GSH to various xenobiotics or electrophiles. The process sacrifices one molecule of GSH for each molecule of xenobiotic so conjugated. While the glutamate and glycine portions are recovered, the cysteine is lost permanently. Excessive activity of GST can cause cysteine and/or glutathione deficiency, oxidative stress, and immune dysregulation.

glycerol-3-phosphate (G3P or H2COH-HCOH-H2C-OPO3--):
an ester of phosphoric acid and glycerol. This compound is used as a shuttle to transport hydrogen atoms into the mitochondria. It is also an important precursor to numerous phosphatides.

glycerol-3-phosphate dehydrogenase (GPD):
the flavoprotein at the mitochondrial membrane which accepts two hydrogen atoms from G3P and transfers them to ubiquinone. GPD activity is upregulated by thyroid hormones and by DHEA. Its function is deficient in many cancers.

glycerol phosphate shuttle:
the transfer sequence which carries reducing equivalents from cytoplasmic NADH to intramitochondrial ubiquinone using G3P as one of the carriers. The complete sequence is: NAD+/NADH...DHAP/G3P...FAD/FADH2...CoQ/CoQH2...cytochromes...O2/H2O

glycine (gly):
the simplest amino acid having no side chain; part of GSH.

glycolysis:
a multistep pathway of glucose metabolism whereby glucose is broken down and eventually converted to pyruvic acid. A small amount of ATP is generated by this process. Under anaerobic conditions puruvate is utilized as the final hydrogen acceptor instead of oxygen thus lactic acid is produced.

glycoside:
one of many compounds altered by covalent attachment to a sugar molecule. The process renders the original compound more water soluble and usually less chemically active.

glycosylated protein(s):
the addition product of monoglyceride to protein. The aldehyde groups of simple sugars in the open configuration can react with the amino groups of numerous proteins to produce imines. While this initial reaction is reversible, subsequent reactions of these imines render the adduct permanent and the affected protein nonfunctional. This problem is prown to occur under conditions of hyperglycemia and accounts for certain degenerative effects of aging and of diabetes.

glyoxal (CHO-CHO):
the simplest dialdehyde composed of two covalently bound aldehyde groups. The two carbonyl groups can conjugate and redox cycle. Nucleophiles such as thiols and primary amines readily add to glyoxal.

glyoxalase:
an enzyme requiring reduced glutathione (GSH) as cofactor which serves to convert alpha-keto-aldehydes to alpha-hydroxy-carboxylic acids. The process occurs in three steps: 1) nonenzymatic addition of GSH to the aldehyde; 2) glyoxylase I shifts two hydrogen atoms from the number one to the number two carbon position; 3) glyoxalase II hydrolyses the intermediate releasing GSH and the alpha-hydroxy-acid.

guanidine (NH2-CNH-NH2):
a highly alkaline amine composed of 2 amino groups and 1 imino group attached to a central carbon atom. Guanidine is a product of the putrifaction of arginine. When present in high levels as in uremia it mildly inhibits mitochondrial function, thus it is a respiratory poison. Other compounds which contain the guanidino group include: methyl guanidine, agmatine, creatine, arginine, streptomycin, cimetidine, guanfacine, aminoguanidine, and metformin.

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