Radioactively labeled compounds unsuitable?

[hivesaeed4]

Some radioactively labeled compounds (such as 32 P-labeled ATP) are not suitable for studies with whole cells because they do not enter cells. Why? The presence of a radioactive isotope does not change the chemical properties of a molecule.

 

[phyzguy]

Some radioactively labeled compounds (such as 32 P-labeled ATP) are not suitable for studies with whole cells because they do not enter cells. Why? The presence of a radioactive isotope does not change the chemical properties of a molecule.

As you said, the isotope does not change the chemical properties, so either this compound does not enter whole cells at all (regardless of whether it is labeled or not), or your information that it doesn't enter whole cells is wrong. Why do you think this?