Lysozomal enzymes

Cathepsin D (EC3.4.23.5). It has been known for more than 20 years that milk also contains an acid proteinase, (optimum pH ss 4.0) which is now known to be cathepsin D, a lysozomal enzyme. It is relatively heat labile (inactivated by 70°C x 10 min). Its activity in milk has not been studied extensively and its significance is unknown. At least some of the indigenous acid proteinase is incorporated into cheese curd its specificity on asl- and / -caseins is quite similar to that of chymosin but it has very poor milk-clotting activity (McSweeney, Fox and Olson, 1995). It may contribute to proteolysis in cheese but its activity is probably normally overshadowed by chymosin, which is present at a much higher level. 

Other proteinases. The presence of low levels of other proteolytic enzymes in milk has been reported (see Fox and McSweeney, 1996). Most of these originate from somatic cells, and their level increases during mastitic infection. The presence of cathepsin D, a lysozomal enzyme, in milk suggests that all the lysozomal proteinases are present in milk although they may not be active. These minor proteinases are considered to be much less significant than plasmin, but more work on the subject is necessary. 

Cameron, T. I., Liten, A. D., Lawrence, J., Farenmark, J., and Turpen, T. H. (1998). Recovery of two recombinant human lysozomal enzymes from plant tissue by expanded bed adsorption with hydrophobic resins. Int. Conf. Expanded Bed Adsorption, 2nd, Napa Valley, CA, 1998, Abstr., p. 10.2. 

CS is an exciting and promising material in tissue regeneration applications as these biopolymers can be easily constructed into various forms and their derivatives are biodegradable by lysozomal enzymes. 

A lipidosis characterized by the presence of increased amounts of sphingomyelin in the tissues. Four types (A-D) have been recognized. In types A and B, a deficiency of the lysozomal enzyme, sphingomyelinase, has been demonstrated. Type A affects the nervous system and carries a poor prognosis. Splenomegaly is the main feature of type B and affected individuals may survive to adulthood. 

Lysozome A membrane-bound organelle in the cytoplasm of most cells containing various hydrolytic enzymes that function in intracellular digestion... 

Weissman G, Bloomgarden D, Kaplan R, et al. A general method for introduction of enzymes by means of immmroglobulin-coated liposomes, into lysozomes of deficient cells. Proc Natl Acad Sci U S A 1975 72 88-92. 

Cathepsin D. The indigenous acid proteinase in milk has received little attention. This activity was first recognized by Kaminogawa and Yamauchi (1972), who isolated and characterized the enzyme and considered it to be similar to the lysozomal acid proteinase, cathepsin D (EC 3.4.23.5). The presence of procathepsin D in milk has been reported (Larsen et al, 1993). Cathepsin D is relatively heat labile (completely inactivated by 70°C X 10... 

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