Comparisons of tryptophan hydroxylase from a malignant murine mast cell tumor and rat mesencephalic tegmentum

A comparative study of the effects of a wide variety of substances on tryptophan hydroxylase from a transplantable murine mast cell tumor and rat brain (mesencephalic tegmentum) was made. Heparin, calcium, limited tryptic proteolysis, sodium dodecyl sulfate, selected phospholipids, and protein phosphorylation each produced activations of tryptophan hydroxylase from rat brain varying from two- to fivefold in magnitude. In contrast to these results, most of these same activators either had no effect (trypsin, phosphorylation) or inhibited the activity of the mast cell hydroxylase (sodium dodecyl sulfate, calcium, phospholipids, phosphorylation). Only heparin activated the mast cell enzyme. The present data taken together with previous results from our laboratory (8) suggest that the tryptophan hydroxylating enzymes from the malignant murine mast cell tumor and rat tegmentum have different molecular, functional, and regulatory properties.