The development and application of label-fracture cytochemistry was pursued. In label-fracture cells fixed or unfixed are labeled and then freeze-fractured. Label-fracture permits the observation in a single, coincident image the distribution of surface receptors and antigens superimposed on conventional Pt/C casts of freeze-fractured membranes. The resolution (5nm attainable) approaches the molecular level. Normal human lymphocytes were label-fractured with monoclonal anti-T3 and anti-T4 antibodies before and alter chemical fixatin by glutaraldehyde. In this work the experiments are designed to map T3 and T4 antigens on the surface, their relation to intramembrane particles revealed by freeze-fracture and their dynamics during capping. We show that while T3 and T4 glycoproteins are associated to IMP domains they do not constitute a structural subset recognizable as a specific cluster of IMPs after capping. In other work we are currently studying the lectin-binding sites in neuronal membranes. We used synaptosomal membrane preparations from rat brain and showed binding sites of concanavalin A and WGA-ovomucoid-gold on the surface associated mainly to IMP domains.
