COMPARISON OF SEROTONIN-PRODUCING MURINE MASTOCYTOMAS, P-815 AND FMA3: DETERMINATION OF TRYPTOPHAN HYDROXYLASE, AROMATIC L-AMINO ACID DECARBOXYLASE, AND CELLULAR CONCENTRATION OF TRYPTOPHAN, 5-HYDROXYTRYPTOPHAN, 5-HYDROXYTRYPTAMINE AND 5-HYDROXYINDOLEACETIC ACID

5-Hydroxytryptamine (serotonin), 5-hydroxytryptophan, tryptophan, and 5-hydroxyindoleacetic acid were determined together with the enzymic activity of tryptophan hydroxylase and aromatic L-amino acid decarboxylase in a comparative way with two lines of transplantable mouse mastocytoma, P-815 and FMA3. These cells had been maintained more than 10 years in our laboratories. 5-Hydroxytryptamine and the other related compounds were determined simultaneously by high performance liquid chromatography (HPLC) with fluorescence detection. The HPLC was also used in the assay of tryptophan hydroxylase and aromatic L-amino acid decarboxylase. For the comparison of tryptophan hydroxylase between the two cell lines, the activity was measured both with and without an in vitro activation by anaerobic preincubation with dithiothreitol. Both lines of the cell contained a large amount of serotonin (1.27 and 0.24 nmol/106 cells in FMA3 and P-815, respectively). The tryptophan hydroxylase activity of FMA3 cells was about one third of that of P-815 when the activity was measured after the activation with dithiothreitol. The activity measured without the activation was comparable in these two cells (0.64 and 0.95 nmol/min/mg protein in FMA3 and P-815, respectively). The biosynthesis of serotonin in P-815 cells was almost completely blocked at the decarboxylation step; the decarboxylase activity of P-815 cells was only 1/400 of FMA3 cells (0.0043 vs.1.53 nmol/min/mg protein).