Lysosomal Acid Hydrolases

Lysosomal acid lipase (EC 3.1.1.13) is a lipolytic enzyme involved in the intracellular metabolism of cholesteryl esters and triacylglycerols derived from plasma lipoproterins (Goldstein et al. 1975). The enzyme is synthesised in a variety of cells, including fibroblasts (Sando and Henke 1982, Sando and Rosenbaum 1985), mononuclear leucocytes 

Acid phosphatase (EC 3.1.3.2) is the classic lysosomal enzyme. The lead substitution method has localised acid phosphatase in the phagosomes of macrophages (Cohn and Wiener 1963) and can be used for electron microscopy. 

Swainsonine reversibly inhibited macrophage lysosomal a-mannosidase (EC 3.2.1.24) in vitro (Greenaway et al. 1983). 

Arylsulphatase (EC 3.1.6.1) from a 96 h rabbit peritoneal exudate macrophage was present in segments of the rough endoplasmic reticulum, and perinuclear cisterna as well as within numerous small vesicles in the Golgi region, probably corresponding to secondary lysosomes (Nichols et al. 1971, Davies and Bonney 1980). 

---

The neuronal ceroid lipofuscinoses (CLN), also referred to as Batten s disease, are a group of disorders characterized by the accumulation of autofluorescent lipopigments. Clinical hallmarks include blindness, seizures, cognitive and motor decline and early death. Age of onset varies from infancy to adulthood. Eight genetic forms have been identified [4]. Two involve lysosomal acid hydrolases. CLN1 codes for palmitoyl protein thioesterase 1. Clinically it presents most often in infancy and leads to loss of active movement and visual contact by 3 years of age. It is most common in Finland, where its incidence is 1 20,000. CLN2 codes for a lysosomal pepstatin-insensitive acid protease. 

Bishayee, S., and Bachhawat, B. K., Interaction between concanavalin A and brain lysosomal acid hydrolases. Biochim. Biophys. Acta 334, 378-388 (1974). 

Following the transfer of the glucosylated mannan cores from dolichol pyrophosphate to the peptide acceptor and the subsequent removal of terminal glucosyl and certain mannosyl residues (see above), there follows a series of reactions in which N-acetylglucosamine is added to the exposed mannosyl terminals and some further removal of mannosyl residues occurs. The general pattern and sequence of these processes has now been substantially proven by the studies of the Kornfelds, Schachter and others. The addition of phosphate to mannose cores occurs in some lysosomal acid hydrolases and is part of a targeting mechanism, considered in detail in Chapter 6. 

Significant differences have been observed between the interactions of several sulphate-containing glycosaminoglycans with particulate lysosomal protein, leading to inhibition of a number of lysosomal acid hydrolases. The order of levels of inhibition is heparin > chondroitin 4-sulphate = chondroitin 6-sulphate > dermatan sulphate. 

It is important to note that most of the results were obtained by treating animals with C. parvum before, simultaneously or just after the inoculation of tumor cells, although in one report (Fisher et al., 1975) antitumor effects of C. parvum were observed on well-implanted tumors. The antitumor effects were shown to be associated with the stimulation of cell-mediated immunity macrophage numbers were increased, their chemotaxis was enhanced, as well as the secretion of lysosomal acid hydrolase (Wilkinson,... 

The inflammatory effect of proteases in rats are inhibited by e-amino-caproic acid, Trasylol and others The clinically useful anti-inflammatory drugs inhibit hyaluronidase and p-glucuronidase. Acetylsallcylic acid inhibits acid phosphatase and cathepsin Gold salts also inhibit synovial lysosomal acid hydrolases ° presumably by binding with sulf-hydryl groups. 

A Comparison of Selected Lysosome Acid Hydrolase Activities in Three Well-Studied Tissue Systems... 

Lysosomal Acid Hydrolase Biosynthesis Induciton of Stimulation... 

Partition of Well-Characterized Lysosomal Acid Hydrolases in Various Tissues... 

Tubular necrosis caused by the release of lysosomal acid hydrolases as a result of aminoglycoside antibiotic overdose... 

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. 

Isopycnic centrifugation. If a post-nuclear extract of hypo-tonically shocked rat TDL is fractionated by means of isopycnic centrifugation in an aqueous sucrose density gradient, all of the sedimentable acid hydrolases, including a small part of cathepsin D, band around a modal density of 1.18 (Fig.l). In agreement with the results presented in Table I, most of the cathepsin D activity is recovered in a soluble, unsedimentable form. The other lysosomal acid hydrolases contribute much less unsedimentable activity. 

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. 

---