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

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?