Abstract
In this study histochemical experiments have been carried out in order to understand the "staining mechanism" of phosphotungstic acid (PTA). One of the main objectives of this project was to investigate the mode of interaction of the heavy metal and to define the type of functional groups in the substrates responsible for PTA binding. Therefore, tissues containing known macromolecules were selected and utilized as model systems. Epiphyseal cartilage, rat sublingual glands, human bone and purified collagen were used to study the interaction of the polyacid with chondroitin sulfate (cartilage), sialic acid (sublingual gland) and collagen (purified collagen and bone). The results obtained suggested that PTA does not interact with chondroitin sulfate, with sialic acid or with the hydroxyl groups of the sugar moieties of these macromolecules. Rather, the binding appeared to be selective for positively charged groups. Since PTA interaction to organic cations was pH-dependent, it is suggested that the heavy metal binds by means of coulombic forces and that no hydrogen bonds are involved.