LC3 is a small 16-18 kDa protein that is found in 3 forms within cells. A pro-form of 125 amino acids becomes cleaved to a 120 amino acid form known as LC3-I. Upon binding to phosphatidylethanolamine (PE), the LC3-II form is generated. LC3-I is found mainly in the cytosol, and LC3-II is found mainly in the membrane fraction.
Upon induction of autophagy by a stress signal such as amino acid starvation, the first step is the formation of autophagosomes.Both LC3-I and LC3-II are seen in healthy cells, but upon induction of autophagy the LC3-II proportion increases as it associates with the membranes of the autophagosomes.
Our Autophagy ELISA Kit (LC3-II Quantitation) uses a selective permeabilization procedure to remove the cytosolic pro-LC3 and LC3-I and retain the autophagosome membrane-bound LC3-II. The quantity of LC3-II in unknown lysates is determined by comparison to a known LC3 standard curve.