Plasma kallikrein possesses a unique protein structure
with four apple domains and a trypsin domain, which evolved
before coagulation factor XI. Tissue kallikreins are trypsinbased enzymes, and some members are highly correlated with
prostate cancer. The evidence that human urine induces hypotension
when injected intravenously into anesthetized dogs was
first described in 1909. Two major kallikreins, plasma kallikrein (KLKB1) and tissue (glandular) kallikrein (KLK),
were found in mammals, and they were transcribed by
different genes. Glandular KLK was an old name and
was replaced by tissue KLK in the modern nomenclature.
