Origin and Dynamics of Lysosomes

Abstract

The lysosomal apparatus, the endoplasmic reticulum, the Golgi apparatus and the secretory and endocytotic vesicles form a system of intracellular organelles delimited by unit membranes. Specific functions can be ascribed to the different elements of that system. Lysosomes are defined functionally as membrane-bound vesicles, in which degradation of macromoleculars is accomplished [1]. To fulfil their function, lysosomes are equipped with degradative enzymes and are accessible for intra- and extracellular material destined for degradation. Both the transfer of lysosomal enzymes and of substrates into lysosomes requires an intensive communication of lysosomes with other parts of the system of intracellular membrane delimited structures [2, 3]. Within that system the synthesis of lysosomal enzymes is completed, newly formed lysosomal enzymes are packaged and material destined for the degradation is transported. Fusion and fission of membrane-bound structures allows the transfer of solutes, membrane parts and membrane-bound material among that membraneous network [4]. Lysosomes are not formed within that membraneous network as complete organelles at once, but acquire their constituents — the lysosomal membrane, the complement of degradative enzymes and the macromolecular substrates — gradually and from various sites.