| Michaelis-Menten constant | <chemistry> The true dissociation constant for the enzyme-substrate binary complex in a single-substrate rapid equilibrium enzyme-catalyzed reaction (usually symbolised by Ks), the concentration of the substrate at which half the true maximum velocity of an enzyme-catalyzed reaction is achieved (when velocities are measured under initial rate and steady state conditions). The ratio of rate constants (k2 + k3)/k1 in the single-substrate enzyme-catalyzed reaction: E + S &dblarr; ES &dblarr; E + products where E represents the free enzyme, S is the substrate, and ES is the central binary complex. The expression for the Michaelis constant will be more complex for multisubstrate reactions. An apparent Michaelis constant is a constant determined either under conditions that are not strictly steady state and initial rate or one that varies with the concentration of one or more cosubstrates. See: Michaelis-Menten equation. Synonym: Michaelis-Menten constant. (05 Mar 2000) |
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| Michaelis-Menten equation | <chemistry> Equation derived from a simple kinetic model for a single-substrate non-cooperative enzyme-catalyzed reaction that successfully accounts for the hyperbolic adsorption isotherm) relationship between substrate concentration and reaction rate. V = Vmax x S/(S + Km), where V is the initial velocity of the reaction, Km is the Michaelis constant, Vmax is the maximum rate approached by very high substrate concentrations and S is the initial substrate concentration. Similar equations can be derived for conditions in which the product is present and for multisubstrate enzymes. Synonym: Victor-Michaelis-Menten equation. (12 Jul 2000) |
| Michaelis-Menten hypothesis | <chemistry> That a complex is formed between an enzyme and its substrate (the O'Sullivan-Tompson hypothesis), which complex then decomposes to yield free enzyme and the reaction products (Brown hypothesis), the latter rate determining the overall rate of substrate-product conversion. See: Michaelis-Menten constant, Michaelis-Menten equation. (05 Mar 2000) |
| michaelmas | The feat of the archangel Michael, a church festival, celebrated on the 29th of September. Hence, colloquially, autumn. Michaelmas daisy. <botany> See Daisy. Origin: Michael + mass religious service; OE. Mighelmesse. Source: Websters Dictionary (01 Mar 1998) |
| Michel Levy scale of retardation colours | <microscopy> Colour chart plotting thickness of the anisotropic specimen, its birefringence (n1-n2) and its retardation in nanometres. Any one of the three variables can be determined if the other two are known. (05 Aug 1998) |
| Micheli, Ferdinando | <person> Italian physician, 1872-1936. See: Marchiafava-Micheli anaemia, Marchiafava-Micheli syndrome. (05 Mar 2000) |
| micmacs | <ethnology> A tribe of Indians inhabiting Nova Scotia and new Brunswick. Alternative forms: Mikmaks. Source: Websters Dictionary (01 Mar 1998) |
| mico | <zoology> A small South American monkey (Mico melanurus), allied to the marmoset. The name was originally applied to an albino variety. Origin: Sp. Or Pg. Mico. Source: Websters Dictionary (01 Mar 1998) |
| miconazole | <chemical> An imidazole antifungal agent that is used topically and by intravenous infusion. Pharmacological action: antifungal agents. Chemical name: 1H-Imidazole, 1-(2-(2,4-dichlorophenyl)-2-((2,4-dichlorophenyl)methoxy)ethyl)- (12 Dec 1998) |
| miconazole nitrate | 1-[2,4-Dichloro-beta-[(2,4-dichlorobenzyl)oxy]phenethyl]imidazole mononitrate;an antifungal agent. (05 Mar 2000) |
| micracoustic | 1. Relating to faint sounds. 2. Magnifying very faint sounds so as to make them audible. Synonym: microcoustic. Origin: micro-+ G. Akoustikos, relating to hearing, fr. Akouo, to hear (05 Mar 2000) |
| micraster | <paleontology> A genus of sea urchins, similar to Spatangus, abounding in the chalk formation; from the starlike disposal of the ambulacral furrows. Origin: NL, fr. Gr. Small + star. Source: Websters Dictionary (01 Mar 1998) |
| micrencephalia | Abnormal smallness of the brain. Synonym: micrencephalia, microencephaly. Origin: micro-+ G. Enkephalos, brain (05 Mar 2000) |
| micrencephalous | Having a small brain. Origin: Micr- + Gr. Brain. Source: Websters Dictionary (01 Mar 1998) |
| micrencephaly | Abnormal smallness of the brain. Synonym: micrencephalia, microencephaly. Origin: micro-+ G. Enkephalos, brain (05 Mar 2000) |