Benders'dictionary of nutrition and food technology

174Many enzymes contain non-protein components which areessential for their function. These are known as prostheticgroups, coenzymes or cofactors and may be metal ions, metalions in organic complexes (e.g. haem in haemoglobin andcytochromes) or a variety of organic compounds, many ofwhich are derived from vitamins.The (inactive) protein withoutits prosthetic group is known as the apo-enzyme, and theactive assembly of protein plus prosthetic group is theholo-enzyme.See also ec numbers; enzyme activation assays; tenderisers.enzyme activation assays Used to assess the nutritional status ofan individual with respect to vitamins b 1 , b 2 and b 6 .A sample ofred blood cells is tested for activity of the relevant enzyme beforeand after adding the vitamin-derived coenzyme; enhancement ofenzyme activity beyond a certain level serves as a biochemicalindex of deficiency of the vitamin in question. The enzymesinvolved are transketolase for vitamin B 1 , glutathione reductasefor vitamin B 2 and either aspartate or alanine transaminasefor vitamin B 6 .enzyme electrodes An immobilised enzyme plus an electrochemicalsensor, enclosed in a probe, used in food analysis andclinical chemistry, e.g. glucose oxidase (EC 1.1.3.4) produceshydrogen peroxide, which can be measured polarographically;lysine decarboxylase (EC 4.1.1.18) produces carbon dioxidewhich can be measured electrochemically.enzyme, immobilized Enzyme bound physically to glass, plastic orother support, so permitting continuous flow processes, or recoveryand re-utilisation of enzymes in batch processes.enzyme induction Synthesis of new enzyme protein inresponse to a stimulus, commonly a hormone, but sometimes ametabolic intermediate or other compound (e.g. a drug or foodadditive).enzyme inhibition A number of compounds reduce the activityof enzymes; sometimes this is a part of normal metabolic regulationand integration (e.g. the responses to hormones), andsometimes it is the action of drugs. Some inhibitors arereversible, others act irreversibly on the enzymes, and thereforehave a longer duration of action (the activity of the enzymeremains low until more has been synthesised).enzyme precursors See zymogens.enzyme repression Reduction in synthesis of enzyme protein inresponse to a stimulus such as a hormone or the presence of largeamounts of the end-product of a pathway.eosinophilia myalgia syndrome Often lethal blood and muscledisorder reported in 1989 among people using supplements of