In EMIT, the enzyme activity is associated with reaction involving which form of antigen?

In EMIT, the enzyme activity is associated with reaction involving which form of antigen?

• A. Free antibody
• B. Free unlabeled antigen
• C. Free labeled antigen
• D. Labeled antigen-antibody complexes

Answer: (C)

In EMIT, the signal comes from the enzyme that is attached to the antigen, and only the antigen that is free (not bound to antibody) can participate in the enzymatic reaction. The test uses competition: unlabeled antigen in the sample competes with the enzyme-labeled antigen for antibody binding. When more unlabeled antigen is present, more antibody is occupied by it, leaving more enzyme-labeled antigen unbound. That unbound, free labeled antigen can react with the substrate, producing the measurable signal. Conversely, when the labeled antigen is bound to antibody, its enzyme activity is inhibited and does not contribute to the signal. So the enzyme activity observed reflects the amount of free labeled antigen in the reaction.

In EMIT, the signal comes from the enzyme that is attached to the antigen, and only the antigen that is free (not bound to antibody) can participate in the enzymatic reaction. The test uses competition: unlabeled antigen in the sample competes with the enzyme-labeled antigen for antibody binding. When more unlabeled antigen is present, more antibody is occupied by it, leaving more enzyme-labeled antigen unbound. That unbound, free labeled antigen can react with the substrate, producing the measurable signal. Conversely, when the labeled antigen is bound to antibody, its enzyme activity is inhibited and does not contribute to the signal. So the enzyme activity observed reflects the amount of free labeled antigen in the reaction.