DETERMINATION OF l-HISTIDINE IN NANOGRAM AMOUNTS AND THE QUESTION OF ITS OCCURRENCE IN MAST CELLS

Abstract

In an attempt to clarify the question of whether histidine is stored in the mast cell for coversion to histamine or whether the rate of conversion is rapid enough to prevent accumulation of histidine so that the rate-limiting step is the histidine uptake, it was found that no histidine was demonstrable in rat peritoneal mast cells by either quantitative analysis or paper chromatographic detection. Microadaptation of Hassall's method, based on conversion of l-histidine by histidase to urocanic acid and measurement of the latter by its absorbance at 277 nm, was made to permit determination of histidine in nanogram amounts in the presence of histamine. This adaptation was found reliable when compared with the o-phthalaldehyde method in estimation of l-histidine in serum and in insulin hydrolysate, and then it was applied to analysis of mast cells before and after l-histidine uptake in vitro. The adaptation should be generally useful in microanalysis of l-histidine in histologically and cytologically defined samples.