NUCLEOSIDE TRANSPORT IN ERYTHROCYTES FROM BOTTLE-NOSED-DOLPHIN (TURSIOPS-TRUNCATUS)

Entry of adenosine, and thymidine, into erythrocytes from adult dolphi ns was rapid, showed saturation at higher substrate concentrations, an d was strongly inhibited by low concentrations of nitrobenzylthioinosi ne (NBMPR). Kinetic parameters were estimated from the concentration d ependence of initial rates of tracer entry at 21 degrees C, as K-m 0.1 4 +/- 0.05 mM and V-max 24.4 +/- 1.9 mu mol/litre cell water/sec for z ero trans entry of adenosine, and K-m 0.96 +/- 0.21 mM and V-max 25.4 +/- 1.7 mu mol/litre cell water/sec for thymidine. Adenosine, and thym idine, entry were inhibited by both purine and pyrimidine nucleosides. Mass law analysis of a saturable component of nitrobenzylthioinosine binding to dolphin red cell membranes gave values of B-max 65.4 +/- 1. 2 pmol/mg protein, and K-d of 1.53 +/- 0.08 nM for a single class of s ites. Photo-irradiation of dolphin red cell membranes in the presence of tritiated nitrobenzylthioinosine led to radioactive labeling of pol ypeptides M(r) 52, 500-58,000, on SDS-PAGE. (C) 1997 Elsevier Science Inc.