Absorption von neutralen und basischen Aminosäuren durch die Körperoberfläche zweier Annelidenarten

Abstract

1. Absorption of L-arginine across the body surface of the oligachaeteEnchytraeus albidus and the polychaeteNereis diversicolor from 10 µM ambient concentrations proceeds at only few percentages of glycine and L-valine uptake rates. Distribution ratios do not exceed equilibrium. InE. albidus L-lysine is transported at the same low rates as observed for L-arginine. 2. InE. albidus the concentration dependent uptake of L-arginine consits of a saturable component and a diffusion component. The saturable component is susceptible to inhibition by structurally analogous substances. This inhibition is strongest in the presence of other basic amino acids and is still significant in the presence of neutral amino acids. Slight inhibition of L-arginine absorption is caused by L-glutamine and L-asparagine, while inhibition of arginine is only inconsiderable in the presence of acidic andβ- andγ-amino acids. Arginine uptake rates are unchanged by organic acids and carbohydrates. 3. Because of nonsusceptibility of arginine transport to metabolic inhibitors (NaCN and ouabain) and Na+-depletion inE. albidus, the saturable component of arginine uptake is regarded to fulfill the requirements for applying the term “facilitated diffusion”, which is discussed in relation to the active transport of neutral amino acids. 4. The mode of basic amino acid absorption is discussed in comparison to that in other animal species and absorbing tissues.