| polymerase chain reaction | <molecular biology, technique> The first practical system for in vitro amplification of DNA and as such one of the most important recent developments in molecular biology. Two synthetic oligonucleotide primers, which are complementary to two regions of the target DNA (one for each strand) to be amplified, are added to the target DNA (that need not be pure), in the presence of excess deoxynucleotides and Taq polymerase, a heat stable DNA polymerase. In a series (typically 30) of temperature cycles, the target DNA is repeatedly denatured (around 90_C), annealed to the primers (typically at 50-60_C) and a daughter strand extended from the primers (72_C). As the daughter strands themselves act as templates for subsequent cycles, DNA fragments matching both primers are amplified exponentially, rather than linearly. The original DNA need thus be neither pure nor abundant and the polymerase chain reaction has accordingly become widely used not only in research, but in clinical diagnostics and forensic science. Acronym: PCR (14 Oct 1997) |
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| MyoD heavy chain kinase | <enzyme> Required for actin activation of the magnesium atpase activity of dictyostelium myosin id (myod); specific for myod Registry number: EC 2.7.1.- Synonym: 110-kD protein kinase, dictyostelium, dictyostelium 110-kD protein (26 Jun 1999) |
| myosin heavy chain | <protein> See myosin: do not confuse with heavy meromyosin which is a subfragment of the heavy chain of myosin II. (18 Nov 1997) |
| myosin light chain | <protein> The light chains of the muscle protein myosin. Each molecule of myosin is composed of two heavy chains and two pairs of light chains. The light chains have a molecular weight of about 20 kD and there is one dissimilar pair of light chains associated with each heavy chain. The proteins all have sequence homology to calmodulin, but not all with calcium binding activity. Several types are known: regulatory light chains (LC 2, DNTB light chains) probably regulate the ATPase activity of the heavy chain directly (through the binding of calcium) or indirectly (activating when they themselves are phosphorylated by myosin light chain kinase) and essential light chains (LC 1, LC 3, alkali light chains), which have a more subtle and apparently nonessential role. In molluscan muscle the EDTA light chains (similar to LC 2 from vertebrate muscle) confer calcium sensitivity on the myosin itself. The light chains are "calmodulin-like" proteins that bind calcium. Two of them can be removed easily, and two with difficulty. The light chains bind the heavy chains in the vicinity of the head groups of the myosin. (12 Dec 1998) |
| myosin light chain kinase | <enzyme> An enzyme that phosphorylates myosin light chains in the presence of ATP to yield myosin-light chain phosphate and ADP, and requires calcium and calmodulin. The 20-kD light chain is phosphorylated more rapidly than any other acceptor, but light chains from other myosins and myosin itself can act as acceptors. The enzyme plays a central role in the regulation of smooth muscle contraction. Chemical name: ATP:myosin-light-chain O-phosphotransferase Registry number: EC 2.7.1.117 (12 Dec 1998) |
| haemolytic chain | The haemolysis that occurs when complement is activated by the previously formed union of erythrocytes and specific antibody. (05 Mar 2000) |
| H chain | <protein> Heavy chain of immunoglobulin, see IgG, IgM, etc. (18 Nov 1997) |
| heavy chain | <protein> In general, the larger polypeptide in a multimeric protein. Thus the immunoglobulin heavy chain is of 50 kD, the light chain of 22 kD, whereas in myosin the heavy chain is very much larger (220 kD) than the light chains (~20 kD). (18 Nov 1997) |
| heavy chain disease | A disorder of immunoglobulin synthesis in which large quantities of abnormal heavy chains are excreted in the urine. The amino acid sequences of the n- (amino-) terminal regions of these chains are normal, but they have a deletion extending from part of the variable domain through the first domain of the constant region, so that they cannot form cross-links to the light chains. The defect arises through faulty coupling of the variable (v) and constant (c) region genes. (12 Dec 1998) |
| xenobiotic medium chain fatty acid - coenzyme A ligase | <enzyme> Partial amino acid sequence of enzyme from bovine liver mitochondria given I first source; has high sequence homology to human and rat sa protein Registry number: EC 6.2.1.- Synonym: xl-i ligase, xl-i carboxylic acid - CoA ligase (26 Jun 1999) |
| short chain | In bacteriology, a string of two to eight cells. (05 Mar 2000) |
| short-chain acyl-CoA dehydrogenase | See: acyl-CoA dehydrogenase (NADPH+). (05 Mar 2000) |
| short-chain beta-hydroxyacyl-CoA dehydrase | <enzyme> Forms trans-2-enoyl-CoA; maximal activity with trans-2-hexenoyl-CoA, followed by crotonyl-CoA; not the same as EC 4.2.1.17 Registry number: EC 4.2.1.- Synonym: beta-hydroxybutyryl-CoA dehydrase, short-chain beta-hydroxyacyl-coenzyme a dehydrase (26 Jun 1999) |
| side chain | A chain of noncyclic atoms linked to a benzene ring, or to any cyclic chain compound, the atoms of an alpha-amino acid other than the alpha-carboxyl group, the alpha-amino group, the alpha-carbon, and the hydrogen attached to the alpha-carbon. (05 Mar 2000) |
| side-chain theory | Ehrlich postulated that cells contained surface extensions or side chains (haptophores) that bind to the antigenic determinants of a toxin (toxophores); after a cell is stimulated, the haptophores are released into the circulation and become the antibodies. See: receptor. Synonym: Ehrlich's postulate. (05 Mar 2000) |