KLK3, also known as APS, is short for Prostate-specific antigen. It is a 261 aa. protein which belongs to the peptidase S1 family and Kallikrein subfamily. This protein has 5 isforms produced by alternative splicing. It is a secreted protein and can forms a heterodimer with SERPINA5 which can inhibit its activity. KLK3 is also strongly inhibited by Zn2+, 100 times more abundant in semen than in serum. This inhibition is relieved by exposure to semenogelins, which are avid zinc binders. KLK3 can hydrolyzes semenogelin-1 thus leading to the liquefaction of the seminal coagulum.
