Membranes were prepared from K562 cells grown in suspension culture and chemically induced to differentiate with hemin. Guanine nucleotide binding assays performed in these fractions showed a 150% increase in GTPγS binding activity of differentiated cell membranes with respect to the control groups. However, immonoblot analysis using specific antibodies indicated that there were no significant differences in the total amounts of G protein subunits between the two groups. Keywords :