Benders'dictionary of nutrition and food technology

217glucostatic mechanism A theory that appetite depends on the differencebetween arterial and venous concentrations of glucose;when the difference falls, the hunger centres in the hypothalamusare stimulated.glucosuria (also glycosuria) Appearance of glucose in the urine,as in diabetes and after the administration of drugs that lowerthe renal threshold.glucuronic acid The acid derived from glucose by the oxidationof the hydroxyl group on carbon-6. Many substances, includinghormones and potentially toxic ingested substances, are excretedas conjugates with glucuronic acid, known as glucuronides. It ispresent in various complex polysaccharides.glucuronides A variety of compounds are metabolised by conjugationwith glucuronic acid to yield water-soluble derivativesfor excretion from the body (see phase ii metabolism).glutamic acid A non-essential amino acid; abbr Glu (E), M r 147.1,pK a 2.10, 4.07, 9.47, codons GAPu. Acidic since it has two carboxylicacid groups; the amide is glutamine.See also monosodium glutamate.glutamine A non-essential amino acid, abbr Gln (Q), M r 146.1,pK a 2.17, 9.13, codons CAPu. The amide of glutamic acid.glutathione A tripeptide, γ-glutamyl-cysteinyl-glycine (GSH).Important in protection against oxidative damage, since it can beoxidised to the disulphide compound (GSSG), which can then bereduced back to active glutathione. Also important in phase iimetabolism of foreign compounds, yielding mercapturic acids asa result of S-conjugation, and in the transport of amino acids intocells.glutathione peroxidase selenium-containing enzyme (EC 1.11.1.9)that protects tissues from oxidative damage by removing peroxidesresulting from free radical action, linked to oxidationof glutathione; part of the body’s antioxidant protection.Low activity in red blood cells indicates selenium deficiency,but not useful as an index of marginal status.glutathione reductase Enzyme (EC 1.6.4.2) that catalyses thereduction of oxidised glutathione (GSSG) to glutathione(GSH), and hence an important antioxidant system. Activationof this enzyme in vitro by added cofactor (flavin adenine dinucleotide,derived from vitamin B 2 ) provides a means of assessingvitamin B 2 nutritional status, sometimes known as the erythrocyteglutathione reductase activation coefficient (EGRAC) test.An activation coefficient above 1.7 indicates deficiency.See also enzyme activation assays.glutelins Proteins insoluble in water and neutral salt solutions butsoluble in dilute acids and alkalis, e.g. wheat glutenin.