TRANSPORT OF GLYCINE AND LYSINE ON THE CHLORIDE-DEPENDENT BETA-ALANINE (B-O,B-+) CARRIER IN RABBIT SMALL-INTESTINE

Transport of glycine, lysine and beta-alanine in rabbit, guinea pig and rat small intestine has been examined by measurements of the unidirectional influx across the brush border membrane of the intact epithelium. In rabbit distal ileum the chloride-dependent fraction of glycine transport, and all sodium- and chloride-dependent lysine transport is carried on the beta-alanine carrier. Lysine eliminates all saturable, sodium-independent transport of glycine. The saturable, sodium-dependent, and lysine resistant influx of glycine is characterized by a K-1/2(Gly) of 60 mM. Glycine transport in the mid intestine of the guinea pig is chloride-independent and in the rat only a minute fraction may be chloride-dependent. These species do not possess an equivalent of the rabbit beta-alanine carrier. In conclusion, glycine transport in rabbit distal ileum is by the sodium-dependent carrier of neutral amino acids, by the sodium-independent lysine carrier, and by the sodium- and chloride-dependent beta-alanine carrier which closely resembles the B-0,B-+ carrier described in mouse blastocysts. All sodium dependent lysine transport in rabbit distal ileum is by the chloride- and sodium-dependent beta-alanine carrier. It is proposed that the beta-alanine carrier in rabbit distal ileum be renamed the B-0,B-+ carrier.