The binding of Vibrio parahaemolyticus 125I-labeled thermostable directhemolysin to erythrocytes.

Thermostable direct hemolysin (TDH) produced by Vibrio parahaemolyticus was iodinated using chloramine T. The 125I-labeled TDH retained up to 80% of the activity of intact toxin. The binding of 125I-TDH to rabbit erythrocytes was inhibited by addition of nonlabeled TDH. The binding of 125I-TDH to rabbit erythrocytes was completed in the 1st or 2nd min of incubation at 37 degrees C in contrast to that at 4 degrees C. 125I-TDH, which cannot lyse horse erythrocytes as does intact TDH, bound to horse erythrocytes as to those of rabbit. The dissociation constants (KD) derived Scatchard plots were 2.85, 4.39, 4.33 and 5.35 x 10-8M for rabbit, horse, human and sheep erythrocytes, respectively. The lytic sensitivity of various erythrocytes to TDH showed no relationship to the binding capacity.