Macromolecules are synthesized and translocated to biomembranes in a specific fashion. Localization of structural proteins, receptors, transport proteins, and enzymes to plasma membrane or subcellular particles is an ordered process giving functionality to the membrane interface or lumen of the structure. Few of the chemical determinants responsible for this organization have been identified. The work focuses on the lysosome as one particle to which a number of proteins and glycoproteins are localized. Studies seek to define structural organization within the particle and list the properties of the lysosomal membrane and translocated protein responsible for that organization. Alteration of these normal processes in lysosomal storage diseases was examined. Study of the biosynthesis and translocation of glucocerebrosidase showed that the glycoprotein enzyme is synthesized on the rough endoplasmic reticulum (ER) and translocated to the lumen of the ER via a leader polypeptide of 2 k Da which interacts with a signal recognition particle (SRP). Cotranslationally, the polypeptide undergoes core glycosylation. This early glycosylated form is the precursor and is a high mannose glycoprotein which undergoes post-translational processing to a complex-type mature form of smaller molecular weight. The protein is neither phosphorylated in the oligosaccharide nor routed to the lysosome via the mannose-6-phosphate pathway. The precursor, intermediate and mature forms of the enzyme can be found as cross-reactive material in cell extracts. This protein polymorphism allows the identification of different mutations in the gene for the enzyme which is responsible for different phenotypes of Gaucher's disease. Ultrastructural immunocytochemistry reveals that the protein does not appear in the lysosome of the neurologically affected variants whereas in the non-neurologically affected phenotypes the catalytically altered protein is present in normal amounts. Altered biosynthesis and translocation of mutant glucocerebrosidase has been defined.
