Hi, I did enzyme substrate reaction by using oxygraphy instrument. I have the crude enzyme concentration and the rate of the reaction, is it possible to calculate enzyme units and activity of the enzyme?
If you can express your data as amount of substrate converted per min, then yes, you can calculate the number of units. You have to decide a unit definition, 1 micromol substrate converted per min ‘under standard conditions’ is the normal definition.
From here, you can get the activity value by taking account of the volume (i.e., units per ml). Don’t forget to multiply by any dilution factors. So, if the enzyme was diluted 1/100 in the assay, you’ll need to multiply by 100 to get the activity in the undiluted extract.
The enzyme concentration (if you mean mg/ml) is not relevant to the above calculations, but it would be if you wanted the specific activity value. In this case you would divide the activity in units/ml by the mg/ml value, to give micromol per min per mg.
Hi Nick,
Thank you so much your response. I have extracted the enzyme by taking initial concentration 50mg/ml solution. From that I took 100ul and diluted to 1ml and I took 100ul of this solution and reacted with 10ul of substrate. Please find the attachment of the graph that obtained from the oxygraph. Can you please help me how can I calculate the enzyme activity and specific activity from this graph. Thank you so much in advance.
There is an official SI unit for enzyme activity which is the KATAL (mol converted per second, be it loss of substrate or appearance of product). Since more than 20 years! So let's get rid of "units".
Respect to Catherine‘s view but almost nobody uses katals. Commercial enzymes are overwhelmingly sold in units. It is also the case that enzyme assays are typically measured in minutes, and the second is therefore too cumbersome. Some SI units never caught on, the katal is one of them.
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