- - active s. that portion of an enzyme molecule at which the actual reaction proceeds; considered to consist of one or more residues or atoms in a spatial arrangement that permits interaction with the substrate to effect the reaction of the latter.- allosteric s. postulated as the place on an enzyme, other than the active s., where a compound, which may be the ultimate product of the biosynthetic pathway involving the enzyme, may bind and influence the activity of the enzyme by changing the enzyme's conformation; the influence of CTP on aspartate carbamoyltransferase activity exemplifies the concept of an allosteric s. on an allosteric protein.- antibody-combining s. SYN: paratope.- antigen-binding s. SYN: paratope.- fragile s. [MIM*136540, MIM*136670] a nonstaining gap at a specific point on a chromosome, usually involving both chromatids, always at the same point on chromosomes of different cells from an individual or kindred; it results in in vitro production of acentric fragments, deleted chromosomes, or other chromosome anomalies; inherited as a dominant chromosome marker.- immunologically privileged sites sites where allografts are not readily rejected or tumors escape immune surveillance probably because these particular areas have poor lymphatic drainage and are not readily accessible to effector cells of the immune system.- ligand-binding s. the s. on a protein's surface that binds a ligand; equivalent to the active s. if the ligand is the substrate of an enzyme.- privileged s. an anatomic area lacking lymphatic drainage, such as the brain, cornea, and hamster cheek pouch, in which heterologous tumors may grow because the host does not become sensitized.- restriction s. a s. in nucleic acid in which the bordering bases are of such a type as to leave them vulnerable to the cleaving action of an endonuclease. SYN: cleavage s..- sequence-tagged sites (STSs) short stretches of DNA sequences that can be detected by use of the polymerase chain reaction.- switching s. the break point in a DNA sequence at which a gene segment unites with another gene segment, as in the production of the immunoglobulins.
* * *site 'sīt n the place, scene, or point of something <the \site of inflammation> see active site
* * *(sīt) a place, position, or locus.
Medical dictionary. 2011.