Subcellular distribution of particle-bound neutral peptidases capable of hydrolyzing gonadoliberin, thyroliberin, enkephalin and substance P.

Subcellular fractions from rat anterior pituitary homogenates were obtained by differential and gradient centrifugation, identified with the help of marker enzymes and screened for peptidases capable of hydrolyzing gonadoliberin, thyroliberin, enkephalin and substance P. Since each neuropeptide is susceptible to cleavage by more than one enzyme, specific substrates or inhibitors have been used for the selective determination of the individual peptidasic activities. Among the various enzymes tested, the angiotensin-converting enzyme, the thermolysin-like metalloendopeptidase ('enkephalinase'), a thyroliberin-degrading enzyme and some aminopeptidasic activities were found to be associated with the plasma membrane. Other aminopeptidases, a gonadoliberin-degrading and a substance-P-degrading enzyme are associated with the mitochondria and thus are most likely not involved in the biological inactivation of neuropeptides.