Abstract
Properties of histidine decarboxylase of rat stomach were studied, including measurements of the Michaelis constant and effects of pH. Optimal conditions for determination of the enzyme were established. A method for this determination on microgram samples of tissue, e.g., microtome sections, that depends on fluorometric analysis of nanogram amounts of histamine, was elaborated and applied to a preliminary investigation of the quantitative histologic distribution of histidine decarboxylase in the body of the glandular stomach of the rat. A parallel study of the quantitative distribution of histamine was also made, and both it and the enzyme activity were predominantly concentrated in the chief cell region. From analysis of gross homogenates, the body of the stomach was found to have greater concentrations of histamine and enzyme activity than the antrum. The findings obtained were considered in relation to distribution of mast cells and acid secretion.