Studies on membrane transport—VII. Transport of histidine through two distinct systems in the tapeworm Hymenolepis diminuta

Abstract

1. 1. In the rat tapeworm, Hymenolepis diminuta, histidine was transported through two kinetically distinguishable systems. One system was inhibited by arginine and one by phenylalanine. A third minor mediated system and diffusion were also distinguished. 2. 2. Arginine and phenylalanine were fully competitive in inhibiting histidine uptake through the respective systems, but arginine and phenylalanine did not interact with one another. 3. 3. Histidine efflux was stimulated by phenylalanine, arginine or histidine and specificities of the efflux systems resembled those of entry systems. 4. 4. The affinities for uptake and efflux of phenylalanine and arginine appeared to be greater for their respective systems than the affinity of histidine for either system.