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.

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.
References in periodicals archive ?
Espejo-Mojica A, Almeciga-Diaz CJ, Rodriguez A, Mosquera A, Diaz D, Beltran L, Diaz S, Pimentel N, Moreno J, Sanchez J, Sanchez OF, Cordoba H, Poutou-Pinales RA, Barrera LA, Human recombinant lysosomal enzymes produced in microorganisms, Molecular Genetics and Metabolism, 2015.
A major finding from past and ongoing newborn screening projects is the much higher than expected prevalence of infants with low lysosomal enzyme deficiencies and genotypes suggestive of later onset disease variants (2).
Salimath, "Effect of curcumin and quercetin on lysosomal enzyme activities in streptozotocin-induced diabetic rats," Clinical Nutrition, vol.
Brown WJ, Farquhar MG (1984) The mannose-6-phosphate receptor for lysosomal enzymes is concentrated in cis Golgi cisternae.
In addition, cells of patients with mucolipidosis IIIA (pseudo-Hurler polydystrophy) showed decreased activity of GlcNAc-1-phosphotransferase at 37[degrees]C and mucolipidosis IIIC cells exhibit defective recognition of lysosomal enzymes caused by mutation of [gamma]-subunit.
Palekar and Magar (10) reported increased activity of four lysosomal enzymes viz.
Ethanol consumption alters trafficking of lysosomal enzymes and affects the processing of procathepsin 1 in rat liver.
When any one of the pro-inflammatory signals activates neutrophils, they not only produce oxygen radicals, but also release a number of other cytotoxic factors, including lysosomal enzymes, cytokines and arachidonic acid metabolites.
Younkin and his colleagues treated normal nerve cells with chemicals known to block lysosomal enzymes.
A property of HuCNS-SC is that they spread throughout the brain and produce both of the lysosomal enzymes missing in the subtypes of Batten disease being studied in the clinical trial.
Autophagy is a dynamic process where aberrant intracellular organelles and macromolecules, including accumulated lipids, are sequestered into double-membrane vesicles called autophagosomes to be delivered to and fused with lysosomes, wherein they are degraded by lysosomal enzymes, and the eventual recycling of macromolecules occurs [1,2].
Classical lysosomal storage diseases (LSDs) (4) are a collection of at least 50 inborn errors of metabolism resulting from a deficiency in the function of lysosomal enzymes and transporters (1).

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