A basic overview of lysosomes

It has been found that there are more than 50 acidic hydrolases (up to 2006) in lysosomes, including proteases, nuclease, phosphatase, glucosidase, lipase, phosphatase and sulfuric acidase. These enzymes control the digestion of a variety of endogenous and exogenous macromolecules. Thus, the lysosomes have the function of dissolving or digesting for intracellular digestive organs.

In the rat liver, a particle fraction containing a hydrolytic enzyme was obtained from a slightly lighter region than the mitochondrial region and named as a lysosome (lss) in the sense that it could be lyso. The enzymes in the lysosomes are acid phosphatases, ribonucleases, deoxyribonucleases, cathepsins, aryl sulfatases, B-glucuronidase, acetyltransferases, etc., which have the optimum pH in the acidic region Of the hydrolase group. According to the electron microscope, the lysosomes are particles or vesicles having a diameter of 0.4 microns to several microns surrounded by a single layer of 6 to 8 microns thick. Because of its extremely diverse form, the acid phosphatase activity is identified as a lysosome.

Lysosomal formation process

The primary lysosomes are formed on the trans side of the Golgi apparatus in the form of budding, and the formation process is as follows.

Endoplasmic reticulum ribosomal synthesis of lysosomal protein → into the endoplasmic reticulum for N-linked glycosylation modification, lysosomal enzyme protein first with three glucose, 9 mannose and 2 N-acetylglucosamine , After resection of three molecules of glucose and a molecule of mannose→ into the Golgi Cis mask capsule → N-acetylglucosamine phosphate transferase to identify lysosomal hydrolase signal spots → transfer of N-acetylglucosamine phosphate in 1 ~ 2 mannose residues → cleavage of N-acetylglucosamine from N-acetylglucosidase in the middle membrane capsule to form M6P ligand → binding to receptor on trans-membrane capsule → selective packaging into primary lysase body.

The main features of lysosomes

(1) lysosomal membrane protein mostly glycoprotein, lysosomal membrane surface with a negative charge. It helps to keep the enzyme in the lysosome free. This is important for exercising normal function and preventing the cells themselves from being digested;

(2) All hydrolytic enzymes had the best activity at pH = 5, but the pH in the surrounding cytoplasm was 7.2. The lysosomal membrane contains a specific transporter that can pump the H + (hydrogen ions) in the cytoplasm by the energy of ATP hydrolysis to the lysosome to maintain its pH5;

(3) Only when the hydrolyzed material enters the lysosome, the enzymes in the lysosomes perform their decomposition. Once the lysosomal membrane is broken, the hydrolytic enzyme escapes, resulting in cell autolysis.

The role of lysosomes

Lysosomes have two functions: First, with the food bubble fusion, the cell swallowed into the food or pathogens and other large particles of material digestion into biological macromolecules, the residue through the efflux of cells discharged; the second is in the cell differentiation process , Some of the aging organelles and biological macromolecules into the lysosome and be digested, which is the body's own re-organization needs.

The main role of lysosomes is digestion, is the intracellular digestive organs, cell autolysis, defense and the use of certain substances are related to lysosomal digestion.

Intracellular digestion: For higher animals, the cellular nutrients are mainly derived from macromolecular substances in the blood, and some macromolecules enter the cells through endocytosis, such as endocytosis of low liposomes to obtain cholesterol, for some single cell Nuclear, lysosomal digestion is even more important.

Apoptosis: Individual processes often involve the transformation or reconstruction of tissues or organs, such as metamorphosis of insects and frogs. This process is achieved under the control of genes, called programmed cell death, destined to eliminate the cells in the form of budding form of apoptotic bodies, macrophages phagocytosis and digestion.

Autophagy: the elimination of cells in the useless biological macromolecules, aging organelles, etc., such as many biological macromolecule half-life only a few hours to several days, liver cells in the average life expectancy of about 10 days.

Defensive effects: If macrophages can swallow pathogens, kill and degrade pathogens in lysosomes.

Involved in the regulation of the secretion process, such as the degradation of thyroglobulin into active thyroxine.

The formation of sperm acrosome: acrosome is equivalent to a chemical drill, soluble in the cortex of the egg, so that sperm into the egg.

All white blood cells contain lysosomal particles that destroy the invading microorganisms. However, there are some pathogens (such as leprosy bacillus, Mycobacterium tuberculosis, etc.) can withstand the role of lysosomal enzymes, which can survive in macrophages. Lysosomes are also important in pathology. As the lung macrophages phagocytosis of inhaled silicon or asbestos dust, causing lysosomal rupture and the release of hydrolytic enzymes, stimulate the increase in connective tissue fibers, leading to the occurrence of silicosis. Tissue hypoxia (such as myocardial infarction) can also cause acute release of lysosomes, so that the concentration of enzymes in the blood increased rapidly.

Further study of lysosomes and tumors

Lysosomes and the relationship between the tumor has attracted increasing attention, generally have the following views:

(1) carcinogenic substances caused by cell division regulation dysfunction and chromosome aberration, may be related to the role of lysosomal release of hydrolase;

(2) some substances that affect laryngeal membrane permeability, such as croton oil, certain detergents, hyperbaric oxygen, etc., is to promote the role of carcinogenic factors, can also lead to abnormal cell division;

(3) in the case of incomplete nuclear membrane, the nuclear membrane of nuclear protection is lost, lysosomes can dissolve chromatin, and cause cell mutation;

(4) some of the products in the process of lysosome metabolism are the basis of tumor cell proliferation;

(5) carcinogens into the cells, before integration with the chromosome, is always stored in the lysosome, which has been confirmed by autoradiography.

In short, lysosomes and tumor occurrence is directly related to the need for further exploration.