Lysosomes and Lysosomal Disorders

Abstract

Lysosomes are organelles with a single membrane. They are present in almost all types of body cells. Their number varies greatly from one cell to another, depending on its type and function. They display a considerable structural heterogeneity and appear in all shapes, sizes and densities. They have been given their name because they are small bodies (soma=body) containing various enzymes that are hydrolytic (lysis= dissolution). These hydrolytic enzymes, hydrolases, catalyze reactions in which macromolecules and macromolecular structures are broken down into smaller components. One of the hydrolytic enzymes contained in lysosomes, is acid phosphatase. This enzyme is most easily tested for using histochemical techniques, and its demonstration in a membranous organelle is usually taken as proof that the organelle is a lysosome. Other lysosmal enzymes are proteases, nucleases, glycosidases, lipases, phospholipases, sulfatases and phosphatases. Between 40 and 50 different enzymes have been identified. These give the lysosome the ability to digest almost all types of macromolecules present in biological material, such as proteins, polysaccharides, lipids and nucleic acids. The low molecular components, that are released, are transported to the cytoplasm to be reutilized. The lysosomal membrane is necessary in order to separate the hydrolytic enzymes from the rest of the cytoplasm and to prevent lysis of components of the cytoplasmic matrix. The acidic interior of lysosomes provides a favorable environment for the digestive activities of the enzymes.