Specific activity

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In nuclear sciences and technologies, "activity" is the SI quantity related to the phenomenon of natural and artificial radioactivity (the SI unit of "activity" is becquerel, Bq, while that of "specific activity" is Bq/kg). For its use in radiochemistry, see radioactivity. Moreover in thermodynamics, thermochemistry and electrochemistry the "activity" is the dimensionless ratio between the fugacity of a chemical species in actual to standard conditions.

Specific activity is the number of enzyme units per ml divided by the concentration of protein in mg/ml. Specific activity values are therefore quoted as units/mg. Specific activity is of no relevance as far as setting up assays is concerned, though it is an important measure of enzyme purity and quality . Activity values (units/ml) are far more important for assay set up since the amount of substrate converted is determined by the number of enzyme units added. Note: It is impossible to calculate the volume of enzyme required for an assay from the specific activity value alone, since the specific activity values for an undiluted enzyme and a 1/1000 dilution are identical. Both the units per ml and mg per ml have been reduced by the same factor

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