Anyone know what is specific activity? (enzymes)

[pieruvate]

I am finding glucanase with highest activity. All the papers I searched with "glucanase characterization" end up having a value called specific activity, with unit u/mg. However, U, according to wikipedia, is the amount of enzyme that catalyses the conversion of one micromole of substrate per minute under the specified conditions of the assay method, and u/mg, the specific activity, is a measurement of enzyme's purity. I do not understand how U, a measure of activity, is divided by mg and suddenly become a measurement of purity. Any thoughts?

 

[Hornbein]

I am finding glucanase with highest activity. All the papers I searched with "glucanase characterization" end up having a value called specific activity, with unit u/mg. However, U, according to wikipedia, is the amount of enzyme that catalyses the conversion of one micromole of substrate per minute under the specified conditions of the assay method, and u/mg, the specific activity, is a measurement of enzyme's purity. I do not understand how U, a measure of activity, is divided by mg and suddenly become a measurement of purity. Any thoughts?

The purer the enzyme, the more active it is per milligram.

 

[Cepacia]

Unless you've purified the enzyme, you will have other protein, etc. in the material that includes the enzyme. U/mg is effectively the ratio of the amount (as activity - assumes the more enzyme in that mg, the greater activity) of the single protein enzyme to the total material in the enzyme prepration (enzyme + other proteins + whatever else).
Example from Sigma

β-Glucanase from Trichoderma longibrachiatum​

>1.0 U/mg
> 10% protein
A mixture composed mainly of β-1→3 / 1→4-glucanase, xylanase, and cellulase activities. β-glucosidase, β-xylosidase, α-L-arabinofuranosidase, amylase, and protease activities are also present.[3][4]
Silicon dioxide 1-<5%
https://www.sigmaaldrich.com/US/en/product/sigma/g4423