Labelling of erythrocyte spectrin in situ with phenylisothiocyanate

The labelling of erythrocyte spectrin in situ with the hydrophobic reagent phenylisothiocyanate (Sigrist, H. and Zahler, P. (1978) FEBS Lett. 95, 116-120) is studied. Spectrin isolated from erythrocytes which have been incubated with phenylisothiocyanate is covalently modified by the probe. The modification in the spectrin molecule is stable under an excess of nucleophile in alkaline conditions. The labelling is very little or not affected by preincubation of erythrocytes of membranes with the polar, structural analogue of phenylisothiocyanate, p-sulfophenylisothiocyanate. When erythrocyte ghosts are subjected to labelling, a substantial increase in the degree of spectrin modification is observed. Subunits of labelled spectrin separated electrophoretically show similar amounts of attached label.