RICIN-BINDING PROPERTIES OF ACID-HYDROLASES FROM ISOLATED LYSOSOMES IMPLIES PRIOR PROCESSING BY TERMINAL TRANSFERASES OF THE TRANS-GOLGI APPARATUS

Acid hydrolases were isolated from the lysosome fraction of .beta.-galactosidase-deficient human fibroblasts and from the mannose 6-phosphate containing medium in which they were grown. Nearly half of the total .beta.-hexosaminidase and .beta.-glucuronidase from both sources bound to Ricin specifically. Lysosomal .beta.-hexosaminidase, metaboically labeled with [35S]-methionine, was also fractionated on Ricin-agarose. SDS-PAGE of immunoprecipitates from Ricin-binding and non-binding fractions revealed approximately equivalent amounts of cross-reacting material at the appropriate MW. We interpret these results to mean that acid hydrolases which are segregated to lysosomes are exposed to trans-Golgi processing enzymes to about the same extent as enzymes which are secreted, and that segregation by the Man 6-P receptor occurs after transit through the trans-Golgi compartment.