Summary. K +, Rb +, or Cs + complexes of valinomycin form ion pair complexes with picric acid and trinitrobenzenesulfonate (TNBS). The formation of a picrate-K +-valinomycin complex is supported by spectral evidence. These complexes have zero net charge and readily permeate the intact erythrocyte membrane. The K+-valinomycin complex has been used to convert the nonpenetrating TNBS into a penetrating covalent probe, making it as useful vectorial probe to measure accessible amino groups of proteins and phospholipids on both sides of the erythrocyte membrane.The enhanced transport of TNBS into the cell by valinomycin is dependent on external K § in the medium. The entry of TNBS into the cell is manifested by an increased labeling of hemoglobin and membrane phosphatidylethanolamine (PE).Stilbeneisothiocyanatedisulfonate (SITS) and anilinonaphthalenesulfonate (ANS) inhibit both the basal and K +-valinomycin stimulated labeling of PE and hemoglobin by TNBS. The data suggest two independent effects of ANS and SITS, one mediated by an inhibition of the anion transport protein and another by the incorporation of these hydrobic anions into the cell membrane with an increase in negative charge on the membrane which leads to an inhibition of TNBS permeation into the cell by electrostatic repulsion.In order to determine the asymmetry of amino-phospholipids in cell membranes, two different chemical probes have been used. One probe readily penetrates the membrane and labels aminophospholipids on both sides of the membrane. The second probe does not penetrate the membrane to any significant extent and labels aminophospholipids on the exterior surface only. These two probes must have different chemical properties since one penetrates and one does not penetrate the cell. Indeed the penetrating probe is usually nonionic and hydrophobic whereas the nonpenetrating probe is anionic. This creates inherent difficulties in chemical reactivity and solubility of the probes which opens to question a direct comparison of the degree of labeling of membrane components by these two probes. If a method were developed

The acridine orange (AO) binding to the deoxyribonucleoprotein (DNP) complex of individual normal lymphocytes, infectious mononucleosis (IM) lymphoid cells and leukaemic blast cells was determined by microfluorometry. Increased AO binding to DNP was found with increasing cell density on the slide and was similar in the different cell populations. staining Only in exceptional cases of IM, the AO binding was high irrespective of cell density. The increased AO binding was due to changes in the DNP complex, which might be induced by the release of macromolecular substances from the cells. The results show that in clinical cytological studies, the fluorescence intensities cannot be used for the discrimination between normal and malignant cells.