The Mechanism of Enzyme Secretion by the Cell

Preparation of rat parotid slices in cold medium caused extensive leakage of amylase during subsequent incubation. Enzyme secretion, by slices not prepared in the cold, was almost absolutely dependent on the addition of an inducer such as epinephrine. Both epinephrine and norepinephrine were more effective than other agents tested. Since epinephrine was apparently consumed during incubation, a sufficient excess of the hormone was required to achieve a maximal yield of enzyme secreted into the medium. Further experiments indicated that 3′5′cyclic AMP is an intermediate in the induction of enzyme secretion by epinephrine. The dibutyryl and monobutyryl derivatives of cyclic AMP caused amylase secretion at a rate which was even slightly higher than that obtained with epinephrine. An initial lag period was apparently due to the slow penetration of such compounds into the cell. β‐hydroxybutyrate was the only substrate which maintained a linear rate of amylase secretion up to termination of the process. The reaction stopped within 40–60 minutes when about 50% of the amylase which had been in the slice was secreted into the medium. This amount corresponded roughly to that located in the intracellular zymogen granules at zero time. Inhibitors of oxidative phosphorylation prevented enzyme secretion and caused some release of enzyme from the intracellular zymogen granules into a soluble pool within the slice. Enzyme secretion apparently required the continuous supply of energy since dinitrophenol was inhibitory even when added after onset of the process. EDTA caused discharge of amylase, presumably by releasing an endogenous inducer.