THE BINDING OF VIBRIO-PARAHAEMOLYTICUS I-125 LABELED THERMOSTABLE DIRECT HEMOLYSIN TO ERYTHROCYTES

Thermostable direct hemolysin (TDH) produced by Vibrio parahaemolyticu s was iodinated using chloramine T. The I-125-labeled TDH retained up to 80% of the activity of intact toxin. The binding of I-125-TDH to ra bbit erythrocytes was inhibited by addition of nonlabeled TDH. The bin ding of I-125-TDH to rabbit erythrocytes was completed in the Ist or 2 nd min of incubation at 37 degrees C in contrast to that at 4 degrees C. I-125-TDH, which cannot lyse horse erythrocytes as does intact TDH, bound to horse erythrocytes as to those of rabbit. The dissociation c onstants (K-D) derived from Scatchard plots were 2.85, 4.39, 4.33 and 5.35 x 10(-8) M for rabbit, horse, human and sheep erythrocytes, respe ctively. The lytic sensitivity of various erythrocytes to TDH showed n o relationship to the binding capacity.