THE USE OF THIOL-SUBSTITUTED CARBOXYLIC ACIDS AS HISTOCHEMICAL SUBSTRATES

Abstract

Thiobutyric, thiocaproic and thiocaprylic acids were synthesized, and enzyme histochemical methods were developed using these thiol-substituted carboxylic acids, as well as thiolacetic acid, as substrates with Pb⁺⁺ as the capture reagent. The localization of final product of these histochemical reactions, PbS, was studied and compared in a variety of tissues with light microscopy. The enzymatic activities demonstrated were sensitive to low concentrations of E600. The localization of these reactions in several intensely reactive tissues, liver, testis and intestine, were also studied with electron microscopy. At a fine structural level, the final product was deposited primarily in relation to the membranous elements of the smooth and rough varieties of the endoplasmic reticulum, including the nuclear envelope, and of mitochondria. The results of these experiments are discussed, including the possible identity of the enzymes concerned with the hydrolysis of the thiol-substituted substrates. It was suggested that at least three activities were demonstrated in these experiments, one of which was the B type esterase of microsomes, and all of which functioned in lipid metabolism.