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netLibrary - eBook Summary Structure-based Drug Design by ...

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Figure 1<br />

Diagram of the human kinin-kallikrein system including the native ligands for B1 and B2<br />

receptor subtypes.<br />

feedback loop. The cleavage of bradykinin from HMWK is highly localized since pre-kallikrein and<br />

substrate (HMWK) circulate as a complex.<br />

Page 120<br />

Another kinin, Lys-bradykinin (also known as kallidin), is produced via the action of the tissuekallikrein<br />

enzyme on LMWK. This enzyme is found in many tissues, either in the form of a precursor<br />

requiring activation or as an active enzyme. In contrast to plasma kallikrein, which preferentially acts<br />

upon HMWK, tissue kallikrein can release kallidin from either HMWK or LMWK. Through the action<br />

of aminopeptidases, kallidin can subsequently be converted directly into bradykinin. This enzyme is<br />

present in both the plasma and on the surface of epithelial cells.<br />

Both bradykinin and kallidin can be degraded <strong>by</strong> a variety of plasma and cell surface enzymes<br />

(kininases) [7]. The most widely recognized of these enzymes are kininase I, kininase II (angiotensin<br />

converting enzyme, ACE), and carboxypeptidase N. In plasma, kininase I cleaves the C-terminal<br />

arginine from both bradykinin and kallidin to form [des-Arg 9] kinins. These [des-Arg 9] kinins are known<br />

to act as agonists of B1 receptors that are present in some species and have been implicated in the<br />

pathophysiology associated with prolonged inflammation [8–10].<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_120.html (1 of 2) [4/5/2004 4:56:27 PM]

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