Transport of selenoamino acids and their sulfur analogues across the intestinal brush border membrane of pigs.

Transport of selenomethionine (Se-Met) and its sulfur analogue, methionine (Met), across the pig jejunal brush border membrane (BBM) was investigated using isolated BBM vesicles. Experiments were also performed to gain insight into the transport mechanism(s) for selenocystine. Se-Met as well as Met were transported by a single, Na+-dependent, carrier-mediated process common for both amino acids. Evaluation of the kinetic parameters revealed no differences between Se-Met and Met in the maximal transport velocity (Vmax) or in the Michaelis constant (Km). Furthermore, transport of Se-Met and Met showed similar characteristics with respect to electrogenicity and substrate specificity. In addition, evidence was obtained for a competitive inhibition of cystine transport across the BBM by selenocystine and basic amino acids.