COLLOIDAL IRON USED AT pH'S LOWER THAN 1 AS ELECTRON STAIN FOR SURFACE PROTEINS

Abstract

The effects of hydrochloric acid on stability, charge and selective affinity of the colloidal ferric hydroxide were studied. The charge was tested electrophoretically. The stability was controlled by measuring the turbidity. The affinity was determined by applying colloid to gelled agarose sections containing hyaluronic acid, polyvinyl sulfate or polylysine. Affinity was also determined by applying the colloid to free tumor cells previously submitted to various types of chemical and enzymatic treatments (esterification, acetylation, periodic acid-hydroxylamine method; neuraminidase, phospholipase C, hyaluronidase) and to isolated rat liver surface membranes pretreated by lipid extraction or incubated with phospholipase C. It was found that the chloride ions at pH's lower than 1 bring about the recharging of the conventional positively charged colloid to a negative form. This negative colloid can be used as a new cytochemical method at the electron microscopic level, to visualize with relative specificity positively ionized groups such as the basic amino groups of protein side chains in the outer and inner hydrophilic leaflets of the cell surface membrane.