Cathepsin enzymic properties

Several lines of evidence indicate that neoplastic cells per se are the main source of extracellular thiol proteinase activity. Recent studies (39) have shown that malignant human breast tumors maintained in organ culture secrete high levels of a cathepsin B-like enzyme into the culture medium. Moreover high levels of cathepsin B-like enzyme are present in the serum of patients with a wide variety of cancers, and these levels decrease when the cancer tissue is removed or treated with therapeutic agents (64, 65). Cathepsin B-like enzyme from cultured cells of malignant tumors (39,66) possesses enzymic properties similar to those of cathepsin B with respect to specificity, affinity, and pH optima for synthetic substrates. It hydrolyzes Bz-Arg-Arg-2-naphthylamide and is inhibited by leupeptin. However, the tumor enzyme is much more stable than cathepsin B to inactivation above pH 7. It has a molecular weight of about 33,000-35,000. The distribution of cathepsin B-like activity was determined in fractions of control and neoplastic epithelial cells from human ectocervix (66). The activity is present mainly in the mitochondrial and lysosomal fractions of normal cells but mainly in the plasma membranes and nuclei of neoplastic cells. 

Relevant heparin-binding enzymes not involved in the coagulation cascade are, for example, elastase, cathepsin G, superoxide dismutase, lipoprotein lipase and other lipases. The plasma clearing properties of heparin are associated with its binding to lipoprotein lipase and hepatic lipase when the enzymes are released from the surface of endothelial cells [11] and have been studied in view of a potential impact on the regulation of atherosclerosis. 

Like SLPI, elafin is a very potent inhibitor of NE. Elafin interacts with elastase in a reversible manner and retains its inhibitory capacity upon dissociation of the complex. Kinetic data have shown that the association rate constant for the formation of an elafin-elastase complex is pH dependent [84]. Una is probably due to the bask properties of the inhibitor and enzyme. Elafin also inhibits proteinase 3 but has no effect on cathepsin G, trypsin, or chymotrypsin. This is inloestiitg in view of the fact that SLPI inhibits cathepsin G but la relatively ineffective against proteinase 3. 

It is obvious that as some of the desquamatory enzymes are found within the lamellar lipids, the physical properties of the SC lipids, together with the water activity in this microenvironment, will influence the activity of these enzymes and ultimately desquamation. The differences in SC water concentration profiles between normal and dry skin influence the enzymic reactions in the SC.1 Equally, differences in enzyme activity occur on different body sites. SCCE levels, for instance are lower in the axilla compared with forearm skin 23 Cathepsin D activity is lower on the forehead compared with the forearm,24 yet SCCE levels are the same. Interestingly, differences in SC turnover... 

Elastase activity is not a universal property of proteolytic sulfhydryl-activated enzymes. There are abundant reports in the literature describing the disappearance of elastic fibers in vivo preceding the repair of damaged tissues, but there is no evidence as to how this is brought about. The tissue cathepsins, most of which are SH-activated, have received little systematic study, but Thomas and Partridge (1960) reported that cathepsins extracted from kidney and spleen by the method of De La Haba et al. (1955) did not digest elastin either in the presence or the absence of cysteine. 

These properties contribute to the function of secretory vesicle cathepsin L as a processing enzyme that produces neuropeptides. 

Alzheimer s disease is characterized by plaques in the brain consisting primarily of the 40-42 amino acid amyloid / -peptide (A/ ) [258]. AfS derives from proteolysis of the amyloid precursor protein (APP) by the fS and y sec-retases to create the N and C-termini of the peptide respectively [259]. The / -secretase has recently been identified as a 501 amino-acid transmembrane protein by several research groups [260-263], The enzyme, variously named BACE, memapsin2, and Asp2, is an aspartic protease related to pepsin, cathepsin D, and renin, with all the properties expected of the /i-sccrctasc. 

Cathepsin G. Isoln from human spleen G. Starkey et al, Biochem. J. 155, 255 (1976). Chymotrypsin-like enzyme. Catalytic and immunological properties P. M. Starkey, A. J. Barrett, ibid. 273. 

Mammalian liver and muscle frucose bisphosphate aldolases are also very susceptible to limited proteolysis (5,53-55). Cathepsin B, cathepsin L, and papain catalyze the limited proteolysis of rabbit muscle and rat liver aldolases 50,51). In fact, decrease of aldolase activity in liver is observed during starvation 109) and after administration of lysosome-tropic agents 103). Leupeptin caused an increase in osmotic sensitivity of lysosomes and an increase in the activities of free lysosomal proteinases, such as cathepsin A and cathepsin D, and a moderate increase of cathepsin B and L, and resulted in a decrease in aldolase activity. The molecular properties of aldolase isolated from the livers of control rats and leupeptin-treated rats indicated that the decrease of aldolase activity is attributable to hydrolysis of a peptide linkage(s) near the carboxyterminal of the enzyme. However, care is necessary in determining whether proteolytic modification of enzymes... 

Proteolytic enzymes were originally studied as extracellular digestive enzymes, and the first sources studied were the stomach and pancreas. Later intracellular proteolytic enzymes from nondigestive oi ans were studied. The intracellular proteolytic enzymes from all cells are called cathepsins. The isolation of cathepsins has not been so successful as the isolation of digestive enzymes because of their lower concentrations and greater labilities. In addition to animal sources, both plants and microorganisms have been studied as sources of proteolytic enzymes. Enzymes from these various sources show many different properties. Some of these will be discussed in connection with individual enzymes. 

Cathepsins. Cathepsins are intracellular proteases of animal origin. The occurrence of several such enzymes has been demonstrated in various tissues, including spleen, pituitary gland, kidney, thymus, etc. It is obvious that there is no reason to anticipate that all cathepsins will have similar properties to each other or to any other proteases. Cathepsins have been designated by both Roman numerals and by letters. Some of these enzymes have been identified with enzymes purified independently, as cathepsin III with leucine aminopeptidase. Several are activated by sulfhydryl compounds, some by metals. The isolation of the various cathepsins and studies of their substrate specificities are subjects currently under investigation, but because of the lower concentration of enzyme in the source materials and the number of related enzymes present, this area of investigation has not reached the development of the study of digestive enzymes. 

During the course of studies on lysosomes in rat thoracic duct lymphocytes (TDL), it was found that cathepsin D, a typical lysosomal enzyme in most cells and tissues, did not show the same distribution as the other lysosomal acid hydrolases after fractionation. In this paper, we report some of our findings concerning the unique properties of this rat TDL enzyme. 

Inhibition by antiserum. An intracellular localization for cathepsin D different from that of the other lysosomal acid hydrolases in rat TDL led us to explore some of the biochemical properties of this enzyme. As illustrated in Figure 3, an antiserum prepared in rabbits against rat liver soluble lysosomal enzymes effectively inhibited rat liver cathepsin D, although it did not inhibit the cathepsin D of rat TDL. In this case the incubations were carried out at pH 5 instead of pH 3.6 to avoid dissociation of the antigen-antibody complex. Both rat liver and rat TDL cathepsin D, however, have identical pH activity curves toward denatured bovine hemoglobin as substrate. 

Collegen biomaterials are biocompatible and nontoxic. They are readly available. Their properties have been well-documented, and they can be processed into a variety of forms. However, collagen products suffer from poor reproducability, which highly depends on the source. They are biodegraded both hydrolytically and enzymatically (by collagenase, and other enzymes e.g., elastase, cathepsin G, etc.) and teherefore it is usually difficult to predict their in vivo degradation rates. 

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