EVIDENCE FOR STRICTLY Na+‐DEPENDENT ACCUMULATION OF SERINE AND THREONINE IN BRAIN CORTICAL SYNAPTOSOMES FROM NEWBORN RATS

Abstract Evidence is presented in this paper to show that synaptosomal particles derived from brains of immature rats possess two separate, high‐affinity transport systems for the hydroxyamino acids, serine and threonine. One of these is strictly Na+‐dependent and the other Na+‐nondependent. The Km terms of both of these systems have values in the range of 20 μM. Na+‐dependent uptakes of serine and threonine do not take place in synaptosomal particles isolated from of adult animals.