PROLINE, LEUCINE, AND ALANINE TRANSPORT IN PLACENTAL MICROVILLOUS MEMBRANE-VESICLES PREPARED FROM LATE GESTATIONAL RATS

To characterize the active transport of amino acids across the placent a, uptakes of proline, leucine, and alanine were kinetically examined in placental microvillous membrane vesicles (PMV) prepared from rats i n the late gestational period. Uptake rates of these amino acids in PM V showed saturable hyperbolic curves that obeyed Michaelis-Menten kine tics. Proline, leucine, and alanine transport were demonstrated to be carrier mediated systems with sodium-dependent, -independent, and both manner, respectively. In addition, sodium-dependent L-alanine transpo rt showed two different systems, and new sodium-independent alanine tr ansport system (K-m of 1.12 mM) was observed in rat placenta. From the se results, rat placenta has carrier mediated amino acid transport sys tems, and posseses at least three different transport systems for alan ine.