OXIDATIVE ENZYMES RESPONSIBLE FOR THE CONVERSION OF 3,4-DIHYDROXYPHENYLALANINE TO MELANIN IN THE SMALL INTESTINE OF RODENTS

The known capacity of certain cells in the rodent intestine to convert dopa to melanin has been investigated. The cells become pigmented following incubation in dopa solutions at pH 6.8 for 24 hr, but not when incubated in tyrosine. The reaction is prevented by pretreatment with buffer solution at 100°C and ethylene glycol, but not by buffer at 60°C, ethanol or benzene. The reaction is inhibited by sodium azide, ascorbic acid and catalase, but not by protamine sulphate, 4-chlororesorcinol and sodium diethyldithiocarbamate. These results suggest that the enzyme concerned is a peroxidase. The cells concerned are confined to the lamina propria mucosae, and are found in the connective tissue of the spleen and liver. They are also present in peripheral blood. They are eosinophilic and have an affinity for pyronin. They do not contain chromaffin material, nor do they stain with nuclear fast red. It is concluded that they are granular leucocytes, probably eosinophil granulocytes.