Isolation of a "proline-rich" protein from rat parotid glands following isoproterenol treatment

Prolonged treatment of rats with isoproterenol induces both hypertrophy and hyperplasia of the parotid glands. Daily injections of 5 mg dl-isoproterenol resulted in a 4–6 fold increase in gland wet weight within 7 days. The protein composition of parotid gland homogenates and saliva, as monitored by disc gel electrophoresis, was markedly altered. In particular, the concentration of a proline-rich protein increased dramatically. This protein was purified by Sephadex G-100 chromatography and preparative disc gel electrophoresis and was found to be comprised mainly of four amino acids (moles/100 moles): Pro, 29.5; Glx, 19.3; Gly, 17.1; Asx, 11.9. The molecular weight as determined by sedimentation equilibrium is about 25,000. When ¹⁴C] glucosamine was injected intraperitoneally, a small amount of label was incorporated into the proline-rich protein. Upon stopping the isoproterenol treatment, the parotid glands and the polyacrylamide disc gel patterns of the soluble proteins both return to normal within 10 to 14 days.