5-Hydroxytryptophan decarboxylase activity in rat mast cells

¹ Department of Pathology, University of Chicago, Chicago, Illinois and University of Washington, Seattle, Washington
² Departments of Pathology, University of Chicago, Chicago, Illinois and University of Washington, Seattle, Washington

Mast cells of rats contain, in addition to histamine and heparin, serotonin. This study was undertaken to determine the ability of mast cells to synthesize serotonin. Preliminary experiments demonstrated a positive correlation between mast cell concentration in different rat tissues and 5-hydroxytryptophan decarboxylase activity. An attempt to demonstrate this activity directly in peritoneal mast cells separated from other cells by centrifugation through a high density sucrose solution was unsuccessful. A new method of separating mast cells was developed employing concentrated bovine albumin solution. The mast cells could be centrifuged through this solution; most other cells remained at the interface. Mast cells separated in purities of 40–80% contained decarboxylase activity at a similar level to that of centrifuged unpurified mast cells. Characteristics of the mast cell decarboxylase system were investigated using peritoneal washings which contained 5% mast cells. The decarboxylase was inhibited by substrate concentrations greater than 1 mg/ml. The activity of the decarboxylase system was enhanced by the addition of pyridoxal-5-phosphate. A pH optimum of 7.5 was found for the decarboxylase activity in the cells.

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