Ultrastructural localization of drug binding sites
The need for a high resolution morphological method of identifying drug binding sites has been mentioned by several authors. Electron microscopic autoradiography may identify statisically an organelle as a drug binding site, but in practice has proven unreliable. This is primarily due to the tissue preparatory procedures used in conventional electron microscopy, which denature proteins and extract many proteins and lipid components from the tissue. As the drug binding sites are denatured and/or extracted, drugs are displaced from their “receptors.” Then the drugs are either extracted or attached to an anomolous binding site created by the preparatory procedure. Sjöstrand's minimal denaturation technique is based on a sound physical-chemical rationale and was modified slightly to accommodate the drug localization procedure used in this study.It was found after many experiments that phosphotungstic acid (PTA) at pH7 had the highest specificity for the drugs used in this study and the lowest affinity for biological structures.