Secretion and Regulation of Two Biosynthetic Enzyme Activities, Peptidyl-Glycineα-Amidating Monooxygenase and a Carboxypeptidase, by Mouse Pituitary Corticotropic Tumor Cells*

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Abstract
Secretion of peptidyl-glycine .alpha.-amidating monooxygenase (PAM) activity and enkephalin convertase (a carboxypeptidase B-like enzyme) activity from AtT-20 mouse corticotrope tumor cells was compared with secretion of pro-ACTH/endorphin-derived peptides. Upon stimulation of secretion by corticotropin-releasing factor, a .beta.-adrenergic agonist, or Ba ions, secretion of PAM activity, enkephalin convertase activity, and immunoactive hormone rose in parallel. During inhibition of stimulated secretion with glucocorticoids or Co ions, secretion of PAM activity, enkephalin convertase activity, and immunoactive hormone fell in parallel. No measurable secretion of cytosolic, mitochondrial or lysosomal marker enzymes was detected, indicating that the secretion of PAM activity and enkephalin convertase activity was specific and not a result of cell damage or lysis. The kinetic characteristics, apparent MW and enzymatic properties determined for the secreted enzymes were similar to those for the enzymes from secretory granules. In AtT-20 cells treated with glucocorticoids for up to 8 days, cellular levels of immunoactive ACTH/endorphin-related peptides decresed to one third of control levels. Levels of PAM activity in cell extracts declined in parallel with the levels of hormone. Levels of enkephalin convertase activity, cell protein, lactate dehydrogenase, fumarase and lysosomal carboxypeptidase did not decline in response to chronic glucocorticoid exposure.

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