Influence of isoproterenol on the incorporation in vitro of [3H]-leucine and n-acetyl-[14C]-mannosamine into proteins and glycoproteins of the parotid glands of the mouse.

The in-vitro incorporation of [3H]-Leu in murine parotid glands started rapidly and continued during the whole incubation period of 10 h and was not stimulated significantly by isoproterenol, except during the first half hour. Secretion of [3H]-Leu incorporated was already observed after 30 min and continued up to 10 h. Isoproterenol stimulated the secretion of 3H-labelled protein during the whole period, but maximally after 4 h. Incorporation of [14C]-ManNAc proceeded at a much slower rate than that of [3H]-Leu. It was at least 1 h before incorporated [14C]-ManNAc appeared in the incubation medium. The secretion of [14C]-ManNAc incorporated was increased by isoproterenol between 2 and 6 h. A major part of [3H]-Leu was incorporated in amylase. The electrophoretically slowest moving isoenzyme of amylase incorporated substantial amounts of [14C]-ManNAc, in agreement with the presence of sialic acid in the isoenzyme. The onset of the [14C]-ManNAc uptake in amylase was slow compared to [3H]-Leu uptake. The [14C]-label could be detected in the secreted amylase after at least 4 h of incubation. It is suggested that isoproterenol decreased the incorporation of [14C]-ManNAc relative to that of [3H]-Leu into the secreted amylase.