Sedimentation profiles of rat parotid gland polysomes in sucrose gradients

Fractionation of rat parotid gland in a sucrose -TKM medium, pH 7.6, leads to extensive disaggregation of polyribosomes by the high level of endogenous, free RNase present in the tissue. Previous studies have shown that prior administration of a potent sialogogue to the animals before sacrifice profoundly reduces the tissue RNase activity, thus permitting isolation of ribonucleoproteins which exhibit active protein synthesis in a cell-free system. This report indicates a similar reduction of active RNase in parotid tissue by the crude enzyme inhibitor present in rat liver postmicrosomal supernatant, and also shows that the size distribution of parotid ribosomal aggregates in sucrose gradients in the presence of this inhibitor parallels findings in animals treated with isoproterenol. This technique will be useful in studying shifts in parotid polysome profiles under conditions which affect protein synthesis in the organ and eliminates the need for the use of potent sialogogues whose effects on the parameters under investigation are not fully known.