Plasma kallikrein therefore is composed of a heavy chain and a light chain held together by a disulfide bond. The heavy chain originates from the amino-terminal end of the zymogen and contains 4 tandem repeats of 90 or 91 amino acids.
Plasma kallikrein is formed by combining a large chain with a smaller one, held together by a sulfur bond. This large chain originates from the beginning part of the inactive precursor molecule and comprises four identical segments of 90 or 91 amino acids.