Molecular organization of prolactin granules. II. Characterization of glycosaminoglycans and glycoproteins of the bovine prolactin matrix.

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Abstract
Prolactin (PRL) granules can be isolated from the anterior pituitary gland of adult cows in nearly 50% yield by use of a procedure previously developed for the fractionation of the rat pituitary. Treatment of the isolated bovine granules with 0.2% Lubrol PX results in the solubilization of most membranes present in the fraction but has only a limited effect on the matrices, which remain aggregated and can be recovered and purified by gradient centrifugation. These membraneless PRL granules, studied in detail by morphological and biochemical techniques, contained only small amounts of contaminants (primarily growth hormone granules and small membrane fragments). Sodium dodecyl sulfate polyacrylamide gel electrophoresis revealed that, in comparison with other fractions isolated from the bovine pituitary, the membraneless granules have a simpler polypeptide composition including PRL (.apprx. 85%), growth hormone (.apprx. 8%) and .apprx. 13 minor bands with apparent MW ranging from 80,000-45,000. Many minor bands are accounted for by glycoproteins, as revealed by their binding of 125I-concanavalin A, and 2 are also stained blue by the stains-all procedure, a reaction specific for acidic glycoconjugates. Chemical analyses of the membraneless granule fraction revealed the presence of a heterogeneous mixture of complex carbohydrates. Among glycosaminoglycans, the major component is heparan sulfate, while hyaluronic acid and chondroitin sulfate are present in smaller amounts. Some glycoproteins are sulfated and account for over 50% of the nondialyzable 35S radioactivity found in the fraction isolated from labeled slices. Although the concentration of glycosaminoglycans and glycoproteins is relatively low in membraneless granules, the possibility that their presence in the fraction is largely due to cross-contamination and/or artifactual adsorption could be excluded on 2 grounds. EM radioautography of preparations obtained from [35S]sulfate- and D-[6-3H]glucosamine-labeled slices showed a significant labeling of PRL granules in both intact cells and membraneless granule pellets, and a mixing experiment showed that membraneless granules contain very little macromolecular sulfate radioactivity absorbed from the soluble glycoconjugates present in the pituitary homogenate.