Cytochemistry of colloidal iron binding to the surface of hela cells and human erythrocytes

Summary It seems from the literature that colloidal iron (C.I.) binding sites on cell surfaces cannot be completely removed by treatment with Vibrio Colerae -neuraminidase. We wondered if C.I. particles bind to negative groups other than the carboxyl groups of sialic acids. Using HeLa cells from suspension cultures and fresh human erythrocytes, we examined, with the transmission electronmicroscope, the influence of the following enzymatic and histochemical treatments on C.I. staining: -neuraminidase; hyaluronidase; ribonuclease; -amylase; mild methylation (MM); MM+saponification (Sap.); MM+Sap+MM; MM+Sap+-neuraminidase; active methylation (AM); AM+Sap; AM+Sap+AM; AM+Sap+-neuraminidase; CH₃OH (80%); Sap. It seemed from these experiments that the carboxyl groups of -neuraminidase sensitive sialic acids constitute the majority of binding sites for C.I. to these particular cells. The most interesting candidates for the residual binding of C.I. are carboxyl groups of -neuraminidase resistant molecules, sulfon, sulfin, and sulfate groups.Supported by a grant from the Algemene Spaar- en Lijfrentekas Cancer FundThe authors gratefully acknowledge the technical assistance of L. Baeke, O. Claeys and J. Roels van Kerckvoorde