Chromogranin A (CHGA), also known as pituitary secretory protein I (SP-I), is a member of the granin family of regulated secretory proteins. CHGA shares several protein characteristics common to the granin family: acidic isoelectric point, the capacity to bind calcium ions, the ability to form aggregates and multiple dibasic cleavage sites. Mature human CHGA is 439 amino acids (aa) and contains 10 dibasic, proteolytic cleavage sites, capable of yielding several smaller peptides, each displaying a unique function. CHGA is expressed exclusively in the secretory dense core granules of most normal and neoplastic neuroendocrine cells. A functional binding ELISA assay was conducted to detect the interaction of recombinant human CHGA and recombinant human LHb. Briefly, biotin-linked CHGA was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to LHb-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST 3 times and incubation with Streptavidin-HRP for 30min, then wells were aspirated and washed 5 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37℃. Finally, add 50 µl stop solution to the wells and read at 450 nm immediately. The binding activity of CHGA and LHb was shown in Figure 1, the EC50 for this effect is 0.3 ug/mL.