Proteases human plasma

The quantification of kinins in human tissues or body fluids has been limited due to the inherent difficulties in accurately measuring the concentration of ephemeral peptides. Today HPLC-based and RIA/capture-ELA measurements are established to determine kinins in human plasma, liquor or mine. Serine protease inhibitors need to be added to prevent rapid degradation of the kinins in vitro during sample preparation. Kinins and their degradation products have been studied in various biological milieus such as plasma/ serum, urine, joint fluids, kidney, lung and skeletal muscle [2]. Under normal conditions, the concentration of kinins in these compartments is extremely low for... 

Mature human albumin consists of one polypeptide chain of 585 amino acids and contains 17 disulfide bonds. By the use of proteases, albumin can be subdivided into three domains, which have different functions. Albumin has an ellipsoidal shape, which means that it does not increase the viscosity of the plasma as much as an elongated molecule such as fibrinogen does. Because of its relatively low molecular mass (about 69 kDa) and high concentration, albumin is thought to be responsible for 75-80% of the osmotic pressure of human plasma. Electrophoretic smdies have shown that the plasma of certain humans lacks albumin. These subjects are said to exhibit analbuminemia. One cause of this condition is a mutation that affects spUcing. Subjects with analbuminemia show only moderate edema, despite the fact that albumin is the major determinant of plasma osmotic pressure. It is thought that the amounts of the other plasma proteins increase and compensate for the lack of albumin. 

The human plasma metallo-protease carboxypeptidase N (CPN, arginine... 

Proteolytic enzymes (proteases) are involved in a wide variety of physiological processes including digestion, fertilization, coagulation, and the immune response. Outside of their normal environment, proteases can be extremely destructive and natural human plasma inhibitors inhibit most proteases that escape. Imbalance in protease-protease inhibitor systems can lead to a number of diseases of which pulmonary emphysema is one well-characterized example. This disease results when the protease elastase attacks elas-tin, the major elastic protein in the lung. Considerable effort has been devoted to the synthesis of inhibitors of proteolytic enzymes such as elastase for possible therapeutic use. In the future, specific and selective synthetic protease inhibitors should be useful for treating specific diseases that range from the common cold to chronic disorders such as emphysema. 

Since a major component of all cells is protein, proteases could be very destructive if they were not carefully controlled or compartmentalized. The potential seriousness of uncontrolled proteolysis can be recognized by the fact that ca. 10% of the proteins by weight found in human plasma are protease inhibitors. The currently recognized plasma protease inhibitors are listed in Table I (3,4). In addition to the plasma inhibitors, there are other inhibitors that are more localized and have not been as well characterized. 

Table I. Major Protease Inhibitors of Human Plasma...

Crommentuin KML, Rosing H, Hillebrand MJX et al. (2004) Simultaneous quantification of the new HIV protease inhibitors atzanavir and tipranavir in human plasma by high-performance liquid chromatography coupled with electrospray ionization mass spectrometry. Journal of Chromatography B 804 359-367... 

Rapp and Burtin (Rla) studied the antigenic constituents and enzymatic activity of gastric mucosal extracts by immunoelectrophoresis at pH 8 on agar gel. They found 9 gastric antigens and 4 zones of proteolytic activity. After activation at low pH, these formed active enzymes, of which 3 had antigenic characteristics. Two of these proteases were also discovered in the human plasma. 

L. Dickinson, L. Robinson, J. Tjia, S. Khoo, D. Back, Simultaneous determination of HIV protease inhibitors amprenavir, atazanavir, indinavir, lopinavir, nelfinavir, ritonavir and saquinavir in human plasma by LC—AdS dS, J. Chromatogr. B, 829... 

L. Pang, W. Hsieh, J. Braun, M.P. Gatto, G.J. Matuszewski, B.K. "High-Throughput Simultaneous Determination of the HIV Protease Inhibitors Indinavir and L-756423 in Human Plasma Using Semi-Automated 96-Well Solid Phase Extraction and LC-MS/MS, J. Pharm. Biomed. Anal. 24(2), 291-305 (2000). 

Saeed, S. A., Chadwick, G. R., and Mill, P. J., Action of proteases on human plasma cholinesterase isoenzymes. Biochim. Biophys. Acta 229, 186-192 (1971). 

The human plasma metallo-protease carboxypeptidase N (CPN, arginine carboxypeptidase, anaphylatoxin inactivator, kininase I, EC 3.4.17.3) catalyzes the release of the basic amino acids lysine and arginine from the C-termini of peptides and proteins such as bradykinin and kallidin [95], the anaphylatoxins C3a, C4a, and C5a [96,97], fibrinopeptides 6A and 6D [98], hexapeptide enkephalins [99], protamine [100], and the creatine kinase MM-isoenzyme [101,102]. Its most likely physiological function is to protect the organism from the actions of potent peptides, which may escape from tissues or be released in the circulation. 

Some people have a genetic predisposition to emphysema. This is called familial emphysema. These individuals have been found to have a genetic defect in the gene that encodes the human plasma protein Uj-antitrypsin. As the name suggests, Ui-antitrypsin is an inhibitor of the proteolytic enzyme trypsin. But, as we have seen in this chapter, trypsin is just one member of a large family of proteolytic enzymes called the serine proteases. In the case of the oii-antitrypsin activity in the lung, it is the inhibition of the enzyme elastase that is the critical event. 

Heparin s anticlotting effect is mediated by acceleration of the action of endogenous antithrombin III, a protease that inactivates clotting factors. Patients with genetic deficiencies in antithromhin III are resistant to heparin and prone to thrombosis. Antithrombin 111 isolated from pooled human plasma is available for use in such patients. The answer is (B). 

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