SOLUBLE FORM OF LAMP-II IN PURIFIED RAT-LIVER LYSOSOMES

Lamp II (for lysosomal associated membrane protein II) is an integral type I glycoprotein. It consists of a very large and heavily glycosyla ted luminal domain, a single transmembrane segment, and a short cytopl asmic tail. We show that in highly purified lysosomes from rat liver, Lamp II, immunodetected with a monoclonal antibody on Western blots, i s surprisingly distributed between a membrane bound form and a ''solub le'' form. The partition of the protein between the membrane and the c ontent of lysosomes is strongly pH dependent. The soluble Lamp II popu lation is sensitive to pH dependent aggregation as it is for many lyso somal content enzymes. (C) 1996 Academic Press, Inc.