Sulfated LH subunits and a tyrosine-sulfated secretory protein (secretogranin II) in female rat adenohypophyses: changes with age and stimulation of release by LHRH

Abstract

Sulfated proteins are present in adenohypophyseal secretory granules but their function and structure are still largely unknown. We studied these proteins in homogenates from cow and rat adenohypophyses labeled in vitro with [35S]sulfate, by one-dimensional and two-dimensional polyacrylamide gel electrophoresis followed by fluorography. We found that the heterogeneous neutral-alkaline sulfated components of approximately 22-20 kDa and approximately 20-18 kDa previously described correspond to lutropin alpha and beta subunits sulfated on carbohydrates. During development sulfated lutropin subunits were found at highest levels in anterior pituitary glands of 14-day-old female rats. Secretogranin II, an acidic tyrosine-sulfated secretory protein, whose presence in granules of gonadotrophs has been recently described, had a similar distribution during development. In the 14-day-old female rat glands luteinizing hormone-releasing hormone stimulated the in vitro release of both sulfated lutropin subunits and secretogranin II. This finding further suggests that secretogranin II might be involved in the packaging of the gonadotrophin. Immature female rat adenohypophyses provide a useful approach for studying sulfation, both on carbohydrate and on tyrosine residues, of secretory proteins.