Radioisotope questions - Help to solve radioisotope problems. (Sep/29/2004 )

I am a third year graduate sutudent. I was reviewing radiation problems.
I came up with this one. I will work in this today, but i hope to compare results with someone there.
S35methionine is commercially available at 1000 Ci/mmole. Methionine is present in an 60KDa transcription factor you are studying in 5 copies per proteinmolecule. Assuming 90% counting efficiency, how much incorporation in cpm would be required to obtain 10 ug of transcription factor?
Well , so far i have found that for this problem you need to work in fmoles.
The main formula is in http://members.tripod.com/~albert51/cazz.html I hope somebody can give me some help.

well
hi i'm not tii sure if my reply... but if you get the answer, please tell me...


10 microgram = 6,022,136,651,675,161,576 daltons (source here)
assuming your TF is 60kD you'll have 100 368 944 194 586 molecules of TF. that is 116µmoles of TF (Avogadro : 6.022 141 99 x 1023)

as you have 5met per molecule, you'll have 583µmoles of met.
Hence you need to use 583µmoles of met...
Assuming 1000Ci/mmol are available, you'll get 1000 x 0,583 = 583Ci.
As a curie is 2.22 exp 12 dpm, that will be 1,609 exp 15dpm.

But maybve i've done a mistake