Placental tyrosine transport and maternal phenylketonuria.

Brush border and basal plasma membrane vesicles prepared from normal human placental syncytiotrophoblast have been used to study L-tyrosine transport across placenta in an attempt to investigate the aetiology of the fetal damage found in maternal phenylketonuria. The results suggest that competition for transport with a grossly raised L-phenylalanine concentration at the basal surface of the trophoblast is responsible for the suppressed delivery of L-tyrosine to the fetus across the placenta.