# Radioenzymatic Assay - Calculation (Dec/02/2008 )

Hi! Is there anyone here who is familiar with calculation of enzyme activity using a radioenzymatic assay. I am working on different enzymes and I am planning to use radioisotopes. Say I am determining product formation using tissue homogenates as source of my enzyme and I am getting count per minute data in the end after counting the product form by a liquid scintillation counter. How can I convert these values to enzyme activity (eg. nmol/min/mg protein etc.). Any biochem expert here. Pls help me. Thanks! Glenmer

Be careful not to confuse radioactive counts per minute with enzyme activity per minute.

If you convert the radioactive counts per min into nmol (this is not always straight forward as you need to determine your detector efficiency by running standards) it will then possible to divide by the incubation time and protein content to get enzyme activity.

Good luck

Be careful not to confuse radioactive counts per minute with enzyme activity per minute.

If you convert the radioactive counts per min into nmol (this is not always straight forward as you need to determine your detector efficiency by running standards) it will then possible to divide by the incubation time and protein content to get enzyme activity.

Good luck

Be careful not to confuse radioactive counts per minute with enzyme activity per minute.

If you convert the radioactive counts per min into nmol (this is not always straight forward as you need to determine your detector efficiency by running standards) it will then possible to divide by the incubation time and protein content to get enzyme activity.

Good luck

Hi I know that, Any more useful information. Thanks.

Be careful not to confuse radioactive counts per minute with enzyme activity per minute.

If you convert the radioactive counts per min into nmol (this is not always straight forward as you need to determine your detector efficiency by running standards) it will then possible to divide by the incubation time and protein content to get enzyme activity.

Good luck

Hi I know that, Any more useful information. Thanks.

I have the spec activity of my radio isotope mCi/mmol, radioactive concentration mCi/ml, the cpm data of my samples, cpm data of my standards, incubation time min, protein concentration mg/ml.. what other variables do i need and how to use to these data to compute for the activity. i wanted to make sure if my calculation is right thats why i am asking help. thanks again

That should be all the information; no need to worry about counter efficiency (if you did want to calculate efficiency for a thesis etc use 1Ci = 2.22x10^12 dpm).

mCi/mL ÷ mCi/mmol = mmol/mL and hence the standards can be plotted with cpm vs mmol. From the regression equation the mmol of the sample is calculated. Then simply devide by the incubation time ( = mmol/min) and protein concentration ( = mmol/min/mg).

mCi/mL ÷ mCi/mmol = mmol/mL and hence the standards can be plotted with cpm vs mmol. From the regression equation the mmol of the sample is calculated. Then simply devide by the incubation time ( = mmol/min) and protein concentration ( = mmol/min/mg).

WOW!!! Yes yes! Thanks alot. I did the same thing. Now I can sleep better knowing I did the right calculation. Thank you so much!