The kinetics of the binding of TxA2 and the characteristics of its putative uptake by platelets (plt) were investigated with a radiolabelled structural TxA2 analogue, 125I-PTA-OH, in platelets from 6 male healthy volunteers. The kinetic constants (Kobs, K1 and K-1) were calculated by time-course experiments according to Weiland and Molinoff. The affinity constant (Km) and maximal uptake velocity (Vmax) values for each subject were determined by the double-reciprocal plot of Lineweaver-Burk. The kinetically determined dissociation constant Kd was 10 nmol/l. In the uptake experiments a saturability of the association rate of the non-displaceable binding was observed at increased ligand concentration. Michaelis-Menten type kinetics were obtained and the Vmax was 32.44 fmol/10(8) plt x hour with a Km of 6.39 nmol/l. These observations suggest that the uptake was a carrier-mediated active transport.
|Number of pages||5|
|Publication status||Published - 1990|
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