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Medical Term:

sedimentation constant


Definition: the constant s in the Svedberg equation for estimating the molecular weight of a protein from the rate of movement in a centrifugal field:where M is the molecular weight, R the gas constant, T the absolute temperature, D the diffusion constant (in square centimeters per second), ? the partial specific volume of the protein, and ? the density of the solvent. The constant s, with dimensions of time per unit of field force (s = drb/dt ?2ro where rb is the position at time t, r0 is the position at time 0, and ? is the angular velocity) is usually between 1 × 10-13 and 200 × 10-13 s. The Svedberg unit (S) is arbitrarily set at 1 × 10-13 s and is very often used to describe the sedimentation rate of macromolecules; 4S RNA.

Synonym(s): sedimentation coefficient

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