The human kallikrein family comprises a large group of 15 serine proteases that are synthesized and secreted by various types of epithelial cells throughout the body, including in the skin. Kallikreins are found in serum and as glandular kallikrein in the salivary glands, pancreas and kidneys.
In the blood, kallikrein is present in an inactive precursor, prekallikrein. This is converted into active kallikrein by the blood coagulation factor XII (Hageman factor) or other stimuli.
The kallikrein-kinogen system is a widespread, fast-acting and short-acting system in the organism for dilating the vessels, increasing capillary permeability, promoting leukocyte migration and sperm motility. Kinins increase the formation of prostaglandins and promote glucose utilization of the working muscle by increasing blood flow.
Some kallikreins are diagnostically significant as tumor markers.
Kallikreins convert inactive kininogens into their active forms(kinins). Kinins in turn influence the excitation of sensitive structures (pain). They are also involved in the development of shock states and inflammatory processes. High molecular weight kininogen (HMW kininogen) and low molecular weight kininogen (LMW kininogen) are precursors of polypeptides. They already have an effect. The following kinins are known:
The angiotensin converting enzyme (ACE), also known as kininase II, inactivates a number of peptide mediators, including bradykinin. ACE continues to activate angiotensin. Inhibition of ACE with ACE inhibitors leads to a decrease in angiotensin (a vasoconstrictor), but also to an increase in bradykinin due to reduced degradation (explanation for side effects of ACE inhibitors such as dry cough, pruritus, urticaria or angioedema).