Demonstration of non-neural tryptophan 5-mono-oxygenase in mouse intestinal mucosa

Tryptophan 5-mono-oxygenase was demonstrated and its activity was measured in mucosal extracts of the mouse digestive tract by means of highly sensitive h.p.l.c. detection. The intestinal enzyme was activated by anaerobic incubation with dithiothreitol, as are the enzymes from mouse mastocytoma cells and bovine pineal gland. The dithiothreitol-enhanced activity was highest at the proximal portion of colon followed by that at the duodenum, where the unenhanced activity/enhanced activity ratio was highest. The enzymic and immunochemical properties of the intestinal tryptophan 5-mono-oxygenase were similar to those of the mastocytoma enzyme. In contrast, the intestinal enzyme was immunochemically different from brain tryptophan 5-mono-oxygenase. The possibility that connective tissue and/or mucosal mast cells are responsible for some of the enzyme activity of the duodenal mucosa was ruled out by the demonstration of the activity in extracts from a mast-cell-deficient mutant mouse (W/Wv). The enzyme in the duodenum was found to reside between the upper villus region and the bottom of the crypt, suggesting that it is mainly of enterochromaffin cell and not of submucosal nerve plexus origin.