lysosome

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Lysosome

A digestive structure found within virtually all types of animal cells. Lysosome sizes, microscopic appearances, and other properties vary among different cell types and circumstances owing, in part, to differences in their functions and states. Typical lysosomes are roughly spherical or elongate bodies with largest dimensions of 0.1–1 micrometer or greater; tens to hundreds are present in a single cell.

Each lysosome is bounded by a membrane and contains several dozen different species of digestive enzymes, each of which can sever particular chemical bonds found in natural materials. Most lysosomal enzymes function best in an acid environment. This acidification is accomplished by a proton pump, built into the membrane surrounding the lysosome, which effects the transport of hydrogen ions into the lysosomes. See Cell membranes, Enzyme, Ion transport

Lysosomes digest materials taken into the cell from the outside (a process known as heterophagy) as well as other materials that originate in the cell's own cytoplasm (autophagy). The materials to be digested are ultimately incorporated into the same membrane-bounded compartments as the lysosomal enzymes. Selective degradative products can pass out of the lysosome by crossing the membrane, but the enzymes cannot. This sequestration, which protects the cell, persists because the admixture of the enzymes and the materials to digest takes place through fusion of membrane-bounded compartments.

In heterophagy, the cell takes up particles or molecules by the process of endocytosis, engulfing them in membrane-bounded vesicles or vacuoles that are formed at the cell surface. The endocytosed material enters lysosomes via intermediate membrane-bounded compartments known as endosomes. In higher animals, heterophagy is most prominently used by leukocytes and macrophages. These specialized cells endocytose invasive microorganisms and use endocytosis in clearing debris and disposing of dead or senescent cells. See Cell senescence and death, Endocytosis, Phagocytosis

In autophagy, cells segregate regions of their own cytoplasm within compartments that come to be bounded by single membranes and to receive lysosomal enzymes. Autophagic lysosomes take part in the remodeling of cells as part of the processes of development and during stressful circumstances. They also participate, along with nonlysosomal enzymes and heterophagic lysosomes, in normal turnover of the body's constituents—the balanced synthesis and destruction through which most molecules of most cells are replaced by new molecules.

Genetic defects in lysosomal enzymes and related proteins are known to be associated with a large number of rare disorders in humans and animals (such as Tay-Sachs disease and Niemann-Pick disease type C). Defective lysosomal function leads to storage of particular classes of molecules that cannot be degraded and, in long-lived cells such as neurons, to complex pathogenic cascades with widespread impact on endosomal-lysosomal function, membrane trafficking, and signal transduction. Such disorders are most often fatal. Lysosomes or prelysosomal structures also have been “adopted” as intracellular homes by certain pathogenic microorganisms that avoid or survive the attacks of the lysosomal system. Some strains of viruses, and toxins such as the one responsible for diphtheria, may use endosomes as their route of entry into the cell, penetrating through the endosomal membrane into the surrounding cytoplasm.

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.

lysosome

[′lī·sə‚sōm]
(cell and molecular biology)
A specialized cell organelle surrounded by a single membrane and containing a mixture of hydrolytic (digestive) enzymes.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Tandem mass spectrometry has a larger analytical range than fluorescence assays of lysosomal enzymes: application to newborn screening and diagnosis of mucopolysaccharidoses types II, IVA, and VI.
Effect of collection, transport, processing and storage of blood specimens on the activity of lysosomal enzymes in plasma and leukocytes.
The specific activity of lysosomal enzymes does not depend on the type of salivary glands in both good health and streptozotocin-induced diabetes.
Salimath, "Effect of curcumin and quercetin on lysosomal enzyme activities in streptozotocin-induced diabetic rats," Clinical Nutrition, vol.
There are few studies of liver lysosomal enzymes that act upon proteins and sulfated polysaccharides.
[54.] Brown WJ, Farquhar MG (1984) The mannose-6-phosphate receptor for lysosomal enzymes is concentrated in cis Golgi cisternae.
biOasis Technologies, (TSX-V:BTI), a publically traded biopharmaceutical company, has received notices of allowance for its patent application titled, 'Use of P97 as an Enzyme Delivery System for the Delivery of Therapeutic Lysosomal Enzymes', from the European and Canadian Patent offices, it was reported on Friday.
All lysosomal enzymes have mannose 6-phosphate on the nonreducing termini of their high mannose-type glycans, synthesized by GlcNAc-1-phosphotransferase and [alpha]-N-acetylglucosaminidase (uncovering enzyme) localized in the cis-Golgi and trans-Golgi network, respectively.
In this study, membrane enzymes including AAP and GGT or lysosomal enzymes NAG and [beta]-GD were measured.
(4.) Smith R.J et al ; Nonsteroidal anti inflammatory agents; Regulation of phagocytic secretion of lysosomal enzymes from guinea pig neutrophils; Jl of Rheumatology and experimental therapeutics;1978; 207: 618-629
Furthermore, further lipopoly-saccharide-induced activation of the Kupffer cells, may contribute to the late liver dysfunction and to the increased synthesis of the lysosomal enzymes such as GLU [8].

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