The experiment used γ-³²P-labeled ATP (γ-³²P-ATP).

Why γ-³²P-ATP is used

  • In most biochemical experiments that track phosphate transfer (like kinase assays), the terminal, or gamma , phosphate of ATP is the group that is transferred to substrates such as proteins or nucleic acids.
  • Labeling this outermost phosphate with ³²P lets researchers directly follow where that phosphate goes, because any phosphorylated product will now be radioactive.

Connection to common exam questions

  • In exam-style questions (including MCAT-style practice), when the question asks which type of ³²P-labeled ATP is used to monitor phosphorylation reactions, the correct choice is typically γ-³²P-ATP rather than α- or β-labeled ATP.
  • This matches the biochemical fact that ATP hydrolysis in phosphorylation reactions usually releases inorganic phosphate and leaves ADP, meaning the gamma phosphate is the one that must be labeled to track transfer.

Information gathered from public forums or data available on the internet and portrayed here.