In a laboratory experiment, researchers are investigating the radioactivity of an antibody–protein X precipitate that forms in the extracellular growth medium. If the goal is to measure the binding efficiency of the antibody to protein X, what aspect of the experimental results would be most relevant for determining the amount of antibody bound to protein X?
A. The total volume of the extracellular growth medium.
B. The concentration of protein X in the growth medium.
C. The level of radioactivity of the antibody–protein X precipitate in the growth medium.
D. The color change in the precipitate over time.