Metabolic pool
Two or more compounds that are rapidly interconverted and which exist in equilibrium with one another.

Metabolic turnover
The rate at which molecules of a given species are replaced by newly synthesised molecules of the same type. This can be measured by isotopic labeling.

Metabolism
(Gr. metobolos, to change). The biochemical processes by which nutrients are built up into living matter, or by which complex substances and food are broken down into simple substances. The sum total of physical and chemical changes that occur in a tissue; includes anabolism and catabolism.

Metabolite
1. A low molecular-weight biological compound synthesised by an enzyme-catalysed reaction. 2. A compound essential for a metabolic pathway. A substance synthesised by the organism, or obtained from the environment. Autotrophic organisms take up inorganic metabolites, such as water. CO₂, nitrates and some trace elements from the environment.

Metabolome
The complete collection of metabolic pathways, and/or metabolites in an organism. Metabolome analysis offers a means of revealing novel aspects of cellular metabolism and global regulation, Metabolomics is the study of the metabolome.

Metabolomics
The study of the metabolite profiles in biological samples with an aim to identify, measure and interpret the complex time-related concentration, activity and flux of endogenous metabolites in cells, tissues, and other biological samples such as blood, urine and saliva. The metabolites include small molecules that are the products and intermediates of metabolism, as well as carbohydrates, peptides and lipids.

Metabonome, metabonomics
The quantitative measurement of the dynamic multiparametric metabolic response of living system to pathophysiological stimuli of genetic modification. This concept has arisen from work on the application of ‘H-NMR spectroscopy to study the multicomponent measurement if biofluids, cells and tissues.

Metacentric chromosome
A monocentric chromosome with a central or near central centromere. If the centromere is exactly at the centre. it is categorised as an M-chromosome and if the centromere is not exactly at the center but in the median region, it is classified as n m- chromosome.

Metachromatic leukodystrophy
A lipid storage disease characterised by deficiency of arylsulphatase A or cerebroside sulphatase. The clinical symptoms include abnormalities in gait, hypotonia, ataxia, psychosis and dementia. The adult form presents in the second to fifth decades with slowly progressive dementia, motor dysfunction, speech and emotional difficulties.metal chelate chromatography A special form of affinity chromatography in which an immobilized metal ion such as Cu²⁺ of Zn²⁺ or a transition metal ion is used to bind proteins selectively by reaction with imidazole groups in histidine residues and indole groups in tryptophan residues.

Metalloenzyme
An enzyme that requires a metal atom(s) for normal activity.

Metallome
Refers to the complete inorganic species within a cell or tissue type.

Metallomics
The study of the content of inorganic species within a cell or tissue-type.

Metalloprotein
A protein containing a metal ion as a prosthetic group.

Metallothionein
A protein that binds heavy metals such as cadmium and lead. It functions to detoxify heavy metals.

Metamerism
The division of body into segments, as in insects.

Metamorphosis
The stage in cell division (mitosis or meiosis) in which all the chromosomes lie on the equatorial plane (an imaginary line that bisects the cell).

Metaplasia A change in the pattern of tissue differentiation.

Metaproteomics The large-scale characterisation of the entire protein complement of environmental microbiota at a given point in time.

Metastasis Spread of disease from one part of the body or one organ to another; a characteristic of malignant tumours.

Metformin See biguanides.