Enzyme kallikreins

Bradykinin is a small peptide that is released from a precursor, kininogen, by the action of the proteolytic enzyme kallikrein, which itself is formed from a precursor, prekallikrein, by the action of the blood clotting factor, Xlla (Figure 17.4). Bradykinin is responsible for the pain, vasodilation and increased permeability of the blood vessels by stimulating formation and release of prostaglandins and prostacyclins from the endothelial cells (see Chapter 11). 

The activities of free and poly(l-vinylpyrrolidone)-bound trypsin were compared by Specht et They observed a significantly lower degree of inactivation (selfdigestion) of the polymer-bound enzyme tiian the unbound enzyme. Kallikrein Iws also been attached to poly(l-vinylpyrrolidone) ° ... 

Thi ,DPhe BK [Thi ,DPhe ]-bradykinin. bradykinin-potentiating peptide teprotide. bradykinin potentiator B teprotide. BRADYKININ RECEPTOR AGONISTS act at sites recognizing members and derivatives of the bradykinin family of hormone peptides - kinins - of which bradykinin (BK) and kallidin (lysyl-bradykinin Lys-BK KD) are the main mammalian members. The bradykinin family is distinct from the tachykinin family of peptides, though both have profound hypotensive actions and contract many intestinal and other smooth muscles. Historically, it was noted that the former action was relatively slow-developing, hence the name bradykinin. Notable actions of bradykinin and kallidin are to dilate blood vessels and increase their permeability to plasma proteins, and to stimulate sensory nerve C-fibres. These actions are pro-inflammatory, and reflect the fact that the kinin-formation system is activated in inflammation, and enzymes (kallikreins) form the kinins from blood-borne or tissue precursors (kininogens) on injurious insult. 

The vasoactive kinins and the peptides of the complement system are examples of the short-chain peptide mediators [165]. Bradykinin is formed by the action of the enzyme kallikrein on the plasma protein, a2-macroglobulin [171]. The resulting nonapeptide is a potent vasodilator, causing erythema, swelling, and pain [172]. Additionally, bradykinin activates phospholipase A2, the enzyme responsible for generating the precursor to the lipid mediators [173]. 

Factor Xlla converts prekallikrein to kallikrein and kallikrein cleaves HK to generate bradykinin. There is also an important positive feedback in the system in which the kallikrein generated rapidly converts unactivated factor XII to activated factor XII, and the rate of this reaction is hundreds of times faster than the rate of autoactivation [11]. Therefore, much of the unactivated factor XII can be cleaved and activated by kallikrein. Cl inhibitor inhibits all functions of factor Xlla and it is one of two major plasma kallikrein inhibitors. Thus all functions of kallikrein are also inhibited, including the feedback activation of factor XII, the cleavage of HK, and the activation of plasma pro-urokinase [66] to lead to plasmin formation. Cl inhibitor also inhibits the fibrinolytic enzyme plasmin, although it is a relatively minor inhibitor compared to a2-antiplasmin or a2-macroglobulin. 

Bradykinin is part of the kallikrein-kinin system, which shares a link to the RAAS through angiotensin-converting enzyme. Bradykinin is a vasodilatory peptide that is released in response to a variety of stimuli, including neurohormonal and inflammatory mediators known to be activated in HF.9 As a... 

Aprotinin is a polypeptide consisting of a chain of 58 amino acid residues, which inhibits stoichiometrically the activity of several proteolytic enzymes such as chymotrypsin, kallikrein, plasmin, and trypsin. Aprotinin is obtained from bovine tissues and purified by a suitable process. It is stored as a bulk solution or lyophilized powder. The amount of two related substances des-Ala-des-Gly-aprotinin and des-Ala-aprotinin is determined by CZE with a 100% analysis. The relative migration times are 0.98 for des-Ala-des-Gly-aprotinin and 0.99 for des-Ala-aprotinin, and the specified limits are 8.0 and 7.5%, respectively. 

The kallikrein-kinin system is an enzymatic pathway giving rise to two predominant vasoactive peptides, kallidin and bradykinin. Kallikrein, the enzyme responsible for the formation of these peptides, exists in plasma and tissues. However, circulating levels of the end products, kalhdin and bradykinin, are quite low because the kalhkrein enzymes are present largely in inactive forms. In addition, the short half-life of these peptides (15 seconds) also contributes to low plasma levels. In general, the kinins produce relaxation of vascular smooth muscle and vasodilation. Bradykinin causes... 

It is a naturally occurring proteolytic enzyme inhibitor acting on plasmin and kallikrein. 

Kinins are potent vasodilator peptides formed enzymatically by the action of enzymes known as kallikreins or kininogenases acting on protein substrates called kininogens. The kallikrein-kinin system has several features in common with the renin-angiotensin system. 

The kallikrein-kinin system. Kininase II is identical to converting enzyme peptidyl dipeptidase (ACE). 

Each kinin is formed from a kininogen by the action of a different enzyme. Bradykinin is released by plasma kallikrein, lysylbradykinin by tissue kallikrein, and methionyllysylbradykinin by pepsin and pepsin-like enzymes. The three kinins have been found in plasma and urine. Bradykinin is the predominant kinin in plasma, whereas lysylbradykinin is the major urinary form. 

Another kinin, Lys-bradykinin (also known as kallidin), is produced via the action of the tissue-kallikrein enzyme on LMWK. This enzyme is found in many tissues, either in the form of a precursor requiring activation or as an active enzyme. In contrast to plasma kallikrein, which preferentially acts upon HMWK, tissue kallikrein can release kallidin from either HMWK or LMWK. Through the action of aminopeptidases, kallidin can subsequently be converted directly into bradykinin. This enzyme is present in both the plasma and on the surface of epithelial cells. 

Kinins. These hormones are small peptides that induce contraction of smooth muscles, lower blood pressure (Box 22-D), and increase vascular permeability.176 They also have a function in contact-activated blood coagulation. The most important human kinins are the nonapeptide bradykinin177178 and the related decapeptide lysine-bradykinin (Table 30-4). Other forms such as Met-Lys-bradykinin and Ile-Ser-bradykinin (T-kinin) are also known. The precursors to the kinins, the kininogens,176 are cleaved by the protease kallikrein (Fig. 12-17) or by kallikreinlike enzymes to form the kinins. Kinins are suspected of being important producers of pain in inflammatory conditions such as arthritis.1763... 

Aprotinin is a polypeptide consisting of 58 amino acid residues derived from bovine lung tissues and shows inhibitory activity toward various proteolytic enzymes including chymo-trypsin, kallikrein, plasmin, and trypsin. It was also one of the first enzyme inhibitors used as an auxiliary agent for oral (poly)peptide administration. The co-administration of aprotinin led to an increased bioavailability of peptide and protein drugs [5,44,45], The Bowman-Birk inhibitor (71 amino acids, 8 kDa) and the Kunitz trypsin inhibitor (184 amino acids, 21 kDa) belong to the soybean trypsin inhibitors. Both are known to inhibit trypsin, chymotrypsin, and elastase, whereas carboxypeptidase A and B cannot be inhibited [7,46],... 

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