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Home >> Dictionary of Bioinformatics, Biochemistry, Biotechnology >> Methaemoglobin MetHb - Methylation Specific PCR
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Methaemalbumin
A haemoglobin derivative formed from haematin due to bleeding into the abdominal cavity or acute haemorrhagic pancreatitis. Pancreatic digestion results in conversion of haemoglobin to haematin, which is absorbed and bound to plasma albumin. Methaemalbumin is brown in colour and can be identified spectrophotometrically before or after addition of ammonium sulphide.
Methaemoglobin (MetHb)
An oxidised from of haemoglobin in which the iron is in the Fe3+ form (haemin). It is therefore incapable of oxygen transport. Normally, haemoglobin undergoes autooxidation to from a small amount of methaemoglobin. However, this can be enzymatically reduced back to haemoglobin and less than 1 per cent is present in the erythrocytes. Methaemoglobin is brown in colour and can be identified by spectrophotometry.
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Methaemoglobinaemia
An increase in methaemoglobin concentration that may be either congenital or acquired. Congenital methaemoglobin is due to an inherited deficiency of methaemoglobin reductase or to presence of an abnormal haemoglobin (HbM), which is easily converted to methaemoglobin. Methaemoglobinaemia may be acquired due to ingestion of drugs such as sulphonamides, nitrates used as food preservatives, agricultural fertilisers, drinking water polluted by industry, aniline and other compounds that are absorbed by the skin. The clinical manifestations of methaemoglobinaemia include cyanosis, anaemia, vascular anoxia and death. Treatment involves administration of methylene blue or ascorbic acid, which reduce methaemoglobin to haemoglobin.
Methane
The simplest hydrocarbon made up of one carbon and four hydrogen atoms (CH4). It is a gas produced from carbon dioxide by certain bacteria during the oxidation of fatty acids.
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Methanogenic bacteria
Bacteria that produce methane gas.
Methanol
The alcohol of methane with the formula CH3OH. It is also known as wood alcohol.
Methanophile (methanotroph)
Bacteria that derive energy from the metabolism of methane.
Methicillin
A synthetic derivative of penicillin made by the addition of a dimethoxyphenyl group to the side chain of penicillin. Methicillin is used in infections caused by penicillin-resistant bacteria because it is not degraded by penicillinase.
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Methionine
A sulphur-containing amino acid.
Methionine-enkephalin (met-enkephalin)
A short peptide with the structure Tyr-Gly-Gly-Phe-Met that inhibits neuropeptides called endorphins which function by binding to the opioid receptor in the brain.
Methotrexate
An antibiotic that inhibits the enzyme dihydrofolate reductase (DHFR) required for purine biosynthesis. It is used as a cancer chemotherapeutic agent because it specifically targets cancer cells, which have a high requirement for DHFR and inhibits their growth. Mutation of DHFR leads to resistance to methotrexate. When methotrexate is added to certain cell lines, resistance occurs due to amplification of the DHFR gene. This phenomenon is used in biotechnology to amplify genes cloned near the DHFR gene. Also called amethopterin.
Methotrexate
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Methyl (-CH3)
A hydrophonbic chemical group derived from methane.
Methyl-accepting chemotaxis proteins (MCPs)
A class of bacterial transmembrane proteins involved in chemotaxis. When the cellular domain of the protein binds an attractant substance, the intracellular domain undergoes methylation. On the other hand, if a repellent substance is found, it becomes demethylated.
Methylation
The addition of methyl (-CH3) group(s) to a macromolecule. For example, the addition of a methyl group to cytosine or adenine residues in DNA.
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Methylation specific PCR
A simple, rapid and inexpensive method to determine the methylation status of CpG islands. The approach involves the determination of methylation patterns from very small samples of DNA, including those obtained from paraffin-embedded samples. This is used to analyse abnormally methylated CpG islands in cancer, and imprinted genes.
Methylcellulose
An inert polymer that increases the density of culture medium to maintain growing organisms in suspension.
Methylcobalamin
A metabolically active from of vitamin B12
5- Methylcytosine (5MeC)
A modified form of cytosine to which a methyl group is added by methylases. These residues provide hotspots for mutations. They undergo spontaneous deamination to form thymine.
7-methylguanosine
A derivative of guanosine that is used to ‘cap’ eukaryotic mRNA.
Methylome
The complete set of DNA methylation modifications of a cell. Alterations in the methylome may be linked to aging and cancer, as well as polymorphic variation in populations.
Methyltetrahydrofolate
A form of the B vitamin, folic acid that functions as a coenzyme in methyl group transfer reactions during purine synthesis. It is also involved in the conversion of homocysteine to methionine.
Methyltransferases
Enzymes that catalyses the transfer of methyl groups from S-adenosylmethionine (SAM) to substrates such as nucleic acid precursors.
Metyrapone test
The method of choice to assess the pituitary-adrenal axis. Metyrapone (2-methyl-1,2 bis-[3’-pyridyl]-propan-1-one) inhibits 11b-hydroxylase, the enzyme responsible for the formation of cortisol from 11-deoxycortisol. Metyrapone decreases in cortisol levels, which can cause increased ACTH release by feedback stimulation. There is accumulation of 11-deoxycortisol in circulation, which can be measured as urinary 17-hydroxycorticosteroid. Metyrapone (750 mg) is given orally at 4-hourly intervals for 24 hours. The normal response is a doubling of the basal excretion of 17-hydroxysteroids and an increase in plasma 11-deoxycortisol and ACTH levels. In Cushing’s diseases of pituitary origin and ectopic ACTH syndrome, there is an exaggerated response to metyrapone compared to normal.
Mevalonate
A precursor of cholesterol.
MHC
See major histocompatibility complex.
MHC class I molecule
A molecule encoded by genes of the MHC that participates in antigen presentation to cytotoxic T (CD8+) cells.
MHC class II molecule
A molecule encoded by the MHC genes, which participates in antigen presentation to helper T (CD4+) cells.
MHC molecule
A member of a large family of cell-surface glycoproteins encoded by the genes of the major histocompatibility complex (MHC). MHC molecules bind to the peptide fragments of antigens and present them to T cells to evoke an immune response. See class I MHC molecule, class II MHC molecule
MHC restriction
The ability of T lymphocytes to respond only when the ‘see’ the appropriate antigen in association with “self” MHC class II proteins on the antigen presenting cells.
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