Amino acid carriers at maternal and fetal surfaces of the placenta by single circulation paired-tracer dilution. Kinetics of phenylalanine transport.

The unidirectional uptake into the trophoblast of L-leucine, L-isoleucine, L-phenylalanine, L-tryptophan, L-methionine and L-tyrosine from either the maternal or fetal circulations of an isolated dually-perfused guinea-pig placenta was studied using a single circulation paired-tracer dilution technique. Significant and equal uptakes were found on both sides. L-Phenylalanine uptake kinetics on the fetal side indicated an apparent Km of 17.0 mM and a V of 8.2 mumol/min per g.