Presence of sulfated proteoglycans in prolactin secretory granules isolated from the rat pituitary gland

Abstract

The composition of the segregated content of rat prolactin granules was investigated taking advantage of the fact that these organelles, isolated as a pure fraction, retain their structural organization after solubilization of their limiting membrane by mild detergent treatment. We found that these membraneless granules contain not only the hormone, but also a number of minor macromolecular components including sulfated glycosaminoglycans, which are labeled when pituitary slices are incubated in vitro with [35S] sulfate. In order to characterize the latter components, the isolated radioactive granules were solubilized (by treatment with either a high ionic strength solution orNaOH) and 35S-labeled acidic glycosaminoglycans precipitated by complexing with cetylpirydinium chloride. A high degree of heterogeneity was observed when the ensuing precipitates were analyzed by cellulose acetate electrophoresis: different components were found to co-migrate with authentic heparin and chondroitin sulfate A and C standards. Another component, which accounts for approx. 50% of the glycosaminoglycan-bound radioactivity, might be heparin sulfate. These acidic glycosaminoglycans are linked to peptide moieties to form proteoglycans.