Dose response to S1P of binding of 70-kD N-terminal fragment of fibronectin to confluent MG63 cells. Binding of¹²⁵I-70-kD fragment of fibronectin was determined in the presence of increasing concentrations of S1P. Specific binding was calculated by subtraction of nonspecific binding (in the presence of 500 mg/L unlabeled fibronectin) from total binding and expressed as nanograms of 70-kD fragment bound per milligram of cellular protein. Data represent the average of duplicates that varied by less than 10%.