The glycoproteins that occur in the colloids of senescent porcine pituitary glands are clusterin and glycosylated albumin fragments.

Periodic acid-Schiff-positive colloids occur in the pituitary glands of many vertebrates. These colloids are surrounded by folliculo-stellate (FS) cells and increase dramatically in number and size with age. The characterization of these colloidal substances is necessary for the establishment of FS cell function. In a previous study we showed that these colloids in the senescent pituitary contain a number of glycoproteins; however, the characterization of these glycoproteins has not yet been carried out. To characterize the pituitary colloid, we purified the colloids by centrifugation and Percoll gradient. The isolated colloids were unable to be solubilized in a regular buffer since they were very dense. However, solubilization was accomplished in sodium dodecyl sulfate (SDS) lysis buffer following treatment with exoglycosidase. Analysis using SDS-polyacrylamide gel electrophoresis showed that the porcine pituitary colloids contain four proteins, CP26, CP40, CP48 and CP60, whose estimated molecular weights were 26 kD, 36-43 kD, 48 kD, and 60 kD, respectively. Staining with concanavalin A (ConA) showed that both CP26 and CP40 were glycoproteins. Moreover, N-terminal amino acid sequencing and Western blot analysis revealed CP26, CP48 and CP60 to be porcine albumin while CP40, the major protein in the colloids, proved to be clusterin. Therefore we report here that the glycoproteins that occur in senescent porcine pituitary colloids are of two types, namely, albumin fragments and clusterin.

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