Complementarity determining region cdr

Hypervariable region within the antigen binding site of immunoglobulin molecules and T-lymphocyte antigen receptors. The sequence in this region determines which antigen (epitope) will bind. Also used to refer to the genomic sequence encoding the hypervariable regions.

complementary base pairs The crucial property of DNA is that the two strands are complementary: guanine and cytosine are complementary and pair up through their hydrogen bonds, as are adenine and thymine, which only form two hydrogen bonds (adenine and uracil in RNA).

complementation The ability of a mutant chromosome to restore normal function to a cell that has a mutation in the homologous chromosome when a hybrid or heterokaryon is formed - the explanation being that the mutations are in different cistrons, and between the two a complete set of normal information is present.

complexins Complexin I and complexin II are cytoso-lic proteins involved in the regulation of neurotransmit-ter release, competing with the chaperone protein alpha-SNAP for binding to synaptobrevin as well as the synaptic membrane proteins SNAP-25 and syntaxin, which together form the SNAP receptor (SNARE) complex. Complexin I is a marker of axosomatic (inhibitory) synapses, whereas complexin II mainly labels axodendritic and axospinous synapses, the majority of which are excitatory.

COMT Catechol-O-methyltransferase; EC Enzyme thought to functionally modulate dopaminergic neurons. Catalyses reaction between S-adenosyl methionine and catechol to form S-adenosyyl-L-homocysteine and guiacol, and methylates catecholamines, thereby terminating their signalling activity. There are two functional polymorphisms in humans, with high enzyme activity (COMT Val) and low enzyme activity (COMT Met) variants, although the significance is still unclear.

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