Cathepsin proteolytic activity

The functional proteins in the cell have to be protected in order to prevent premature degradation. Some of the intracellularly active proteolytic enzymes are therefore enclosed in lysosomes (see p. 234). The proteinases that act there are also known as cathepsins. Another carefully regulated system for protein degradation is located in the cytoplasm. This consists of large protein complexes (mass 2 10 Da), the proteasomes. Proteasomes contain a barrel-shaped core consisting of 28 subunits that has a sedimentation coef cient (see p. 200) of 20 S. Proteolytic activity (shown here by the scissors) is localized in the interior of the 20-S core and is therefore protected. The openings in the barrel are sealed by 19-S particles with a complex structure that control access to the core. 

Buchs (B49) reported that extracts from the pyloric antrum and upper duodenum of man show proteolytic activity with two pH optima between pH 1 and 4, of which the second peak at a higher pH is larger than that at a lower one. He considered this, however, as evidence for the presence of pepsin and cathepsin in pyloroduodenal secretion. 

A third proteinase appears to exist in the gastric juice, which exerts proteolytic activity at a neutral pH of about 7.0, i.e., in the range where pepsin and cathepsin no longer are active. The existence of a protease called parachymosin, active at pH 5.0-7.0, has been described in the past (Fig. 1) (see B46). Buchs (JM6) considered it to be an integral part of the gastric protease, the two other components of which were pepsin and cathepsin. In the early thirties, Castle s group found some paral-... 

Secretory leukocyte protease inhibitor is a protein of 11,726 molecular weight, secreted by the parotid gland. First isolated and characterized by Thompson and Ohlsson (7) in 1986, it was found to have a high affinity for leukocyte elastase, cathepsin G and trypsin. The inhibitor is of therapeutic interest in the treatment of disease states that involve leukocyte-mediated proteolysis. Emphysema and cystic fibrosis are examples where severe tissue destruction is caused by uncontrolled proteolytic activity. 

Other denaturing factors are scarcely employed at present. Denatura-tion by acids in polarographic examinations proceeds very slowly moreover, in acidified sera the present proenzymes or enzymes can be activated for example, at pH about 1.8 pepsinogen is activated to pepsin, causing proteolytic cleavage at pH about 3.8, cathepsin is activated or perhaps another pH value can be attained which happens to be most favorable for proteolysis caused by enzymes of catalytic nature (65). These facts could have led in the past to faulty results of polarographic examinations of protein denaturation by acids. 

Enzymological application of polarography was tried in the cerebrospinal fluid, the proteolytic activity being investigated after addition of inactivated serum as substrate (198). A comparison with the serum revealed the presence, in healthy subjects, of the cathepsin system in the cerebrospinal fluid, whereas in the serum two systems are found, viz., those of pepsinogen and cathepsin. The cathepsin activity in the cerebrospinal fluid is about half as high as that in the serum. In the cerebrospinal fluid of newborn infants lower values are found than in that of older children and adults. In 74 examinations no relationship with the diagnosis could be established, so that further study is necessary in this direction. 

Tissues were examined for the proteolytic activity of pepsinogen and cathepsin (246). In simian tissues, proteolysis was tested at pH 1.8. It is impossible to obtain samples of tissues free from blood, which contains pepsinogen, and consequently proteolysis was not evaluated below border values, which could have corresponded to the maximal possible content of blood inherent in the tissues. 

The alignment of them realized in the tetrapetide allows for a simultaneous inhibition of the proteolytic activity of trypsin-like serine proteases, papain-like cysteine proteases, and pepsin-like aspartyl proteases. Therefore, this unique compound represents a blueprint for the design of protease class-spanning inhibitors [85, 86]. The capability of (59) to inhibit proteases belonging to different classes for trypsin, cathepsin B, cathepsin L, and papain was reported (see Table 30.3). Miraziridine A [85] also inhibited cathepsin B with an IC50 value of 1.4 pg/mL. Aziridine-2,3-dicarboxylic acid (14) is a rare natural product, reported from a Streptomyces [36], and vArg has never before reported as a natural product. 

DTT, and EDTA, (4) pepstatin and iodoacetate. The first tube would be expected to reflect the full proteolytic activity of all protein-ases except for metalloproteases the second would be expected to permit only the expression of non-thiol proteases the third would be expected to show no cathepsin D activity, and the fourth would be expected to block all thiol and carboxyl enzymes. Calculations based on these four values were used to estimate the results in Figure 2. 

An example in this category is as follows (8,9) 4.2% carbobenzoxy-glycine and 3.7% aniline incubated with papain at 40° and at pH 4.6 gave an 80% yield of carbobenzoxyglycine anilide. The optimum pH and the necessity for activation by cysteine, glutathione, or HCl were the same as for the hydrolytic action of the enzyme. Acetyl, benzoyl, and carbobenzoxy derivatives of alanine, leucine, and phenylalanine yielded with aniline or phenylhydrazine the corresponding anilides or phenyl-hydrazides. Similar reactions were catalyzed by bromelin and cathepsin, proteolytic enzymes obtained respectively from pineapple and pig liver. Under the conditions which promoted the above syntheses, hippurylamide was completely hydrolyzed there was no synthrais of the amide from hippuric acid and ammonia. 

Lewis, T., Hartmann, C. B., and McCoy, K. L., Gallium Arsenide Modulates Proteolytic Cathepsin Activities and Antigen Processing by Macrophages, J. Immunol., 161, 2151, 1998. 

---