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I am working with the enzyme Cu/Zn Superoxide (SOD1) and i am quantifying them in ng/ml. However, most past studies has SOD1 quantified in unit/mg or unit/ml, and i need to compare the SOD1 level of my study with those past studies. Is there a way to standardize these units?

Thank you!

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You need a value for the specific activity of the purified enzyme, in units/ mg (or similar). Also you need to check on the definition of a unit of activity for your enzyme since this is empirically defined. –  Alan Boyd Feb 16 at 16:17

2 Answers 2

There is no archaism in measuring enzyme amounts in units. Unit definition for SOD and a protocol can be found here (from Sigma): https://www.safcglobal.com/technical-documents/protocols/biology/enzymatic-assay-of-superoxide-dismutase.html :

"One unit will inhibit the rate of reduction of cytochrome c by 50% in a coupled system, using xanthine and xanthine oxidase ..."

I don't think, there is a good way to convert ng's to units, since one measures either mass or enzymatic activity, and the correlation between them is not always consistent. Units should be much more reliable in terms of comparisons with other studies, if you are not considering your enzyme as, e.g., a nutritious substance.

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Quantification is a measure of your protein quantity and units/ml or mg is a unit of protein quantity. These are two different things. You need to set a rxn of SOD with its substrate and get activity which is proportional to your consumption of substrate. Then u will get the activity of your protein which will be in units/mg or ml

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But: This is only valid for a certain batch, since the activity of protein preparations varies between batches. Thats why we have this units, which is not a very good thing. But better than nothing. –  Chris Feb 17 at 13:42
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Right sir....:) –  user5741 Feb 17 at 20:17

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