Kallikrein

Kallikreins (tissue and plasma kallikrein) are a subgroup of the serine protease family.

Functions
They liberate kinins (BK and KD) from the kininogens.

It also generates plasmin from plasminogen:

Prekallikrein is the precursor of plasma kallikrein. It can only activate kinins after being activated itself by factor XII or other stimuli.

Genes
There are 15 known kallikreins: KLK1, KLK2, KLK3, KLK4, KLK5, KLK6, KLK7, KLK8, KLK9, KLK10, KLK11, KLK12, KLK13, KLK14, KLK15

Clinical significance
Kallikreins are targets of active investigation by drug researchers as possible biomarkers for cancer.

Prostate-specific antigen (PSA; hk3, human kallikrein gene 3) and human glandular kallikrein (hK2) are used as tumor markers for prostate cancer.