Kinin–kallikrein system

Kinin–kallikrein system is a complex biochemical system that plays a crucial role in the regulation of various physiological processes, including blood pressure, inflammation, and pain perception. It is composed of several proteins, enzymes, and peptides, the most important of which are kinins and kallikreins.

Overview

The kinin–kallikrein system is activated by the enzyme kallikrein, which cleaves the kininogen proteins to release kinin peptides. These peptides, in turn, bind to kinin receptors on the surface of various cells, triggering a cascade of biochemical reactions that lead to the dilation of blood vessels, increased permeability of capillary walls, and stimulation of pain receptors.

Components

Kallikrein

Kallikrein is a group of serine protease enzymes that are responsible for the activation of the kinin–kallikrein system. They are produced in various tissues, including the kidney, pancreas, and salivary glands.

Kininogen

Kininogen is a protein that serves as the precursor for kinins. It is produced in the liver and circulates in the blood in an inactive form until it is cleaved by kallikrein.

Kinin

Kinin is a group of peptides that are released when kininogen is cleaved by kallikrein. The two main types of kinins are bradykinin and kallidin, both of which are potent vasodilators and mediators of inflammation and pain.

Kinin Receptors

Kinin receptors are proteins located on the surface of various cells that bind to kinins. There are two main types of kinin receptors: B1 and B2. The B2 receptor is constitutively expressed and binds to both bradykinin and kallidin, while the B1 receptor is induced during inflammation and binds to des-Arg9-bradykinin and des-Arg10-kallidin.

Functions

The kinin–kallikrein system plays a crucial role in the regulation of blood pressure, inflammation, and pain perception. It is also involved in the regulation of coagulation, fibrinolysis, and angiogenesis, and has been implicated in the pathogenesis of various diseases, including hypertension, asthma, and cancer.

Clinical Significance

Due to its role in various physiological processes, the kinin–kallikrein system is a target for the development of new therapeutic strategies. Drugs that inhibit the activity of kallikrein or block the binding of kinins to their receptors have been developed for the treatment of hypertension, asthma, and other conditions.

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  Simplified diagram of the Kinin-Kallikrein System