| polarized light microscope | <instrument, microscopy> A microscopical polarizcope, i.e., a compound microscope which is equipped with two polars and a Bertrand lens, chemists and mineralogists are the principal users. (05 Aug 1998) |
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| 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) |
| curing light | <dentistry> A special UV light used to help attach brackets to your teeth (08 Jan 1998) |
| pupillary light-near dissociation | A stronger near pupil response than light response; due to weak pupillomotor input, Argyll Robertson pupil, dorsal midbrain syndrome, or to misdirection of ciliary muscle fibres into the iris sphincter. Synonym: light-near dissociation. (05 Mar 2000) |
| pyramid of light | A triangular area at the anterior inferior part of the tympanic membrane, running from the umbo to the periphery, where there is seen a bright reflection of light. Synonym: cone of light, light reflex, Politzer's luminous cone, red reflex, Wilde's triangle. Malacarne's pyramid, a lobule on the undersurface of the cerebellum, the posterior portion of the vermis. (05 Mar 2000) |
| swinging light test | Test to detect a relative afferent defect in one eye by watching pupillary movements. With the patient fixing in the distance, the light is held on each eye for about a second, and quickly moved to the other eye. Assuming no defect of the innervation to the iris sphincter in one eye (which would produce an anisocoria in light), the eye with the weaker light response has a relative afferent pupillary defect. This asymmetry of pupillomotor input can be estimated by holding neutral density filters in front of the better eye until the pupillary responses of the two eyes are balanced. Synonym: swinging light test. (05 Mar 2000) |
| drummond light | A very intense light, produced by turning two streams of gas, one oxygen and the other hydrogen, or coal gas, in a state of ignition, upon a ball of lime; or a stream of oxygen gas through a flame of alcohol upon a ball or disk of lime; called also oxycalcium light, or lime light. The name is also applied sometimes to a heliostat, invented by Drummond, for rendering visible a distant point, as in geodetic surveying, by reflecting upon it a beam of light from the sun. Origin: From Thomas Drummond, a British naval officer. Source: Websters Dictionary (01 Mar 1998) |
| immunoglobulins, light-chain | Polypeptide chains, consisting of 211 to 217 amino acid residues, isolated from immunoglobulins and having a molecular weight of approximately 22 kD. There are two major types of light chains, kappa and lambda. In man they are found in a ratio of 60% to 40%, respectively. Both chains consist of linear repeating, similar, but not identical, segments of about 110 amino acid residues. In each segment a disulfide bond establishes a tightly folded approximately 60-membered loop or domain. Adjacent domains are linked by less tightly folded regions. Both light chains contain two such domains. Two light and two heavy chains make one immunoglobulin molecule, but both light chains in one ig are of the same type. (12 Dec 1998) |
| incident light | <microscopy> Sometimes denotes any over-stage lighting not included by methods of vertical illumination. (05 Aug 1998) |
| infrared light | See: infrared. Invisible light, historic term for X-rays. (05 Mar 2000) |
| ophthalmoscopy with reflected light | Examination of that part of the fundus adjacent to an area illuminated by a sharply focused light. (05 Mar 2000) |
| tapetal light reflex | The glow from the eyes of some animals in the dark when a light illuminates the retina; due to the reflection of the light from the tapetum, an iridescent layer (containing guanidine crystals) in the choroid. (05 Mar 2000) |
| EDTA light chain | <protein> Myosin light chains (18 kD) from scallop muscle (two per pair of heavy chains), easily extracted by calcium chelation. Although the EDTA light chains do not bind calcium they confer calcium sensitivity on the myosin heavy chains. (18 Nov 1997) |
| transmitted light | <microscopy> The usual method for illuminating transparent microscopic specimens. The light is concentrated on the specimen by the substage condenser. Objects appear in outline (refraction images) or coloured on a bright field (colour images). (05 Aug 1998) |