Sulfated compounds in the zymogen granules of the guinea pig pancreas

Abstract

Sulfate incorporation into the guinea pig pancreas was investigated by light (LM) and electron microscope (EM) autoradiography using a system of minilobules incubated in vitro for 60 min in Krebs-Ringer bicarbonate medium (KRB) containing 35SO4 z-. In acinar cells, examined by EM autoradiography, the label was found concentrated over Golgi elements (including condensing vacuoles) and zymogen granules.35SO42-was also incorporated by the epithelial cells of the entire pancreatic duct system, the incorporation being surprisingly high in the epithelium of the major ducts. In all ductal epithelia, autoradiographic grains appeared over the Golgi complex and the plasmalemma.Since a contribution of the duct epithelium to the sulfated compounds found in the discharged secretion could not be ruled out, a purified zymogen granule fraction was used as a source material for the isolation of sulfated compounds of acinar origin. The presence of 35S-radioactivity in the zymogen granules and condensing vacuoles of this fraction was ascertained by autoradiography (of sectioned pellets). From a lysate of this zymogen granule fraction, a soluble sulfated compound of low isoelectric point and high molecular weight was isolated by gel filtration under conditions that allowed its satisfactory separation from the bulk of the secretory proteins.

Ionic interactions between bovine chymotrypsinogen A and chondroitin sulfate A.B.C.. A possible model for molecular aggregation in zymogen granules.

“…Sulfated polyanions have been proposed as one of the critical interacting species as they satisfy the first requirement (23,16,9). Indeed, autoradiographic studies indicate convincingly that the primary site of SO4 -~ incorporation is the Golgi complex (3,24,18). Given their low pI (resulting from sulfation), such polyanions are expected to interact at neutral pH with cationic proteins, known to be an important fraction of the pancreatic secretion (in the guinea pig, --60% have a pI > 8) (23,21).…”

“…KEY WORDS chymotrypsinogen A 9 chondroitin sulfate glucosaminoglycans molecular aggregation zymogen granule condensation turbidity A sulfated macromolecular fraction has recently been isolated from the zymogen granules of the guinea pig pancreas (17,18). Preliminary results indicate that this fraction is composed of acidic glucosaminoglycans, principally heparan sulfate and chondroitin sulfate (18).…”

“…Preliminary results indicate that this fraction is composed of acidic glucosaminoglycans, principally heparan sulfate and chondroitin sulfate (18). Such compounds have been implicated in the process by which pancreatic acinar cells concentrate their secretory proteins in the condensing vacuoles of the Golgi complex (23,16,9).…”

“…Sulfated polyanions, prepared from guinea pig zymogen granunules as previously described (18), were resuspended in 2 mM Tris maleate buffer, pH 6. Increasing amounts of the ensuing solutions were mixed with ChTg (1 mg/ml) and aggregate formation was monitored by turbidimetry, asS-labeled compounds were mixed with 1 ml of ChTg solution (1 mg/ml) and were precipitated with different amounts of carrier chondroitin sulfate.…”

SLC26 anion exchangers of guinea pig pancreatic duct: molecular cloning and functional characterization

“…Pancreatoliths have not been reported in Slc26a6 Ϫ/Ϫ mice with urolithiasis (22). Slc26a6 may also contribute to ductal sulfate reabsorption (5,40). Moreover, pancreatic oxalosis has been detected in patients with primary hyperoxaluria (12,56), but the role of pancreatic ductal SLC26a6 in ductal oxalate secretion in this setting remains unknown.…”