The enzyme activity measured in EMIT reflects the reaction involving which form of antigen?

The enzyme activity measured in EMIT reflects the 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 label is an antigen attached to an enzyme. The antibody in the assay can bind either to the unlabeled antigen in the sample or to the enzyme-labeled antigen. When the antibody binds the labeled antigen, the enzyme’s activity is blocked, so that complex does not generate a signal. Therefore the enzyme activity that is measured comes from the portion of labeled antigen that remains unbound, i.e., the free labeled antigen. This is why the readout reflects the reaction involving the free labeled antigen. The other forms—free antibody, free unlabeled antigen, or the labeled antigen–antibody complex—do not contribute to the enzymatic signal in EMIT.

In EMIT, the label is an antigen attached to an enzyme. The antibody in the assay can bind either to the unlabeled antigen in the sample or to the enzyme-labeled antigen. When the antibody binds the labeled antigen, the enzyme’s activity is blocked, so that complex does not generate a signal. Therefore the enzyme activity that is measured comes from the portion of labeled antigen that remains unbound, i.e., the free labeled antigen. This is why the readout reflects the reaction involving the free labeled antigen. The other forms—free antibody, free unlabeled antigen, or the labeled antigen–antibody complex—do not contribute to the enzymatic signal in EMIT.