Monoclonal antibodies against integral membrane proteins from lysosomes (LIMPs) have been developed to study the biognesis, turnover and intracellular traffic of these organelles and the problems of sorting implicated in these processes. The results indicate that LIMPs move from the site of their synthesis in the endoplasmic reticulum to the Golgi system. In this organelle they are glycosylated, acquiring N-liniked chains of high mannose and complex carbohydrates while moving through the stack of cysternae in a cis to trans direction with similar rates (30 min). Sorting the delivery of LIMPs to lysosomes occurs from the trans-part of the Golgi system. The process of delivery is not synchronous due to the different times of retention of LIMPs in the trans-Golgi (0-90 min). Once their delivery is produced LIMPs are transported to high density lysosomes specifically, efficiently and rapidly (30 min). Transport involves the budding of small size vesicles loaded with LIMPs (i.e. primary lysosomes) from the tubules of the trans-reticular Golgi. LIMPs are transported to the same lysosomes. Neither the sorting nor the delivery of LIMPs is dependent on N-linked carbohydrates and occurs in the presence of tunicamycin. Carbohydrates play an important role in protecting LIMPs against degradation by proteolyic enzymes in lysosomes, as shown by the fast degradation of LIMPs produced in the presence of tunicamycin. Fully glycosylated LIMPs display different half lives in lysosomes.
