A recently cloned rat kidney protein (NBAT) mediates the sodium-independent transport of neutral as well as basic amino acids and cystine when expressed in Xenopus laevis oocytes. The human equivalent of this transporter may be the one that is defective in cystinuria. Immunocytochemical studies have indicated that NBAT is primarily localized in the brush border membranes of rat kidney and intestinal epithelial cells, a localization consistent with its proposed role in amino acid transport. Two contrasting topological models have been proposed for NBAT: a four membrane-spanning domain (MSD) Nin-Cin model and a single MSD Nin-Cout model. We have investigated the topology of this membrane protein using two different approaches. One method was an immunofluorescent labeling technique in which intact or membrane-permeabilized cells expressing NBAT were probed with antibodies directed against putative extracellular and intracellular domains of the protein. In the second method, fragments generated by limited surface proteolysis of intact brush border membrane vesicles were subjected to immunoblot analysis using several site-specific antibodies. Both approaches yielded results consistent with a four MSD Nin-Cin topological model for NBAT.

By means of immunohistochemical methods, we have investigated the cellular distribution of prothymosin alpha and parathymosin in rat thymus and spleen, using specific antibodies raised against thymosin alpha-1 and against parathymosin. We observed prothymosin alpha immunoreactivity in lymphoid cells both in thymus and spleen. In the thymus, prothymosin alpha staining was more marked in cortex than in medulla. In the spleen, prothymosin alpha was found in lymphocytes of the periarteriolar lymphatic sheaths and was especially prominent in the germinal centers. Parathymosin immunoreactivity in the thymus was mainly localized in the medulla; positive cells were reticuloepithelial cells from the thymic reticulum and the blood barrier. Thymocytes were negative. In spleen, parathymosin was found in reticular cells arranged in a ring between the periarteriolar lymphatic sheath and the marginal zone. Our results do not support an exclusive role for these peptides as immune system hormones or cytokines.

High-titer, site-specific antibodies have been produced against the rat kidney broad-spectrum, sodiumindependent neutral and basic amino acid transporter (NBAATr) whose cDNA we cloned earlier. These antibodies have allowed us to characterize the transporter protein in normal rat tissues and in various cellular and in vitro expression systems. Western analysis detected 84-to 87-kDa glycosylated species enriched in rat renal and jejunal epithelial cell brush border membranes. In vitro translation of NBAA-Tr complementary RNA in the rabbit reticulocyte lysate system yielded a 78-kDa protein, a molecular mass that was predicted by the amino acid sequence deduced from the cloned cDNA. Translation in the presence of rough microsomal membranes yielded a glycosylated 89-kDa species. Glycosylated 87-to 89-kDa species were also expressed in Xenopus oocytes microinjected with NBAA-Tr complementary RNA and in COS-7 cells transfected with NBAA-Tr cDNA. Localization of NBAA-Tr in renal and intestinal brush border membranes is consistent with its proposed role in transepithelial transport of amino acids.

According to gel‐filtration experiments, α‐ and β‐thymosins appear to form oligomers, which are 4‐5‐fold larger than the corresponding polypeptides. However, on analysis by sedimentation equilibrium ultracentrifugation, prothymosin α and thymosin β4 showed relative molecular masses of 12 800 and 4600, which are close to the values calculated from their amino acid sequences, confirming their existence in solution as discrete monomeric entities.

The synthesis of a series of analogs and oligomers of N-(2-aminoethyl)glycine (Aeg) are described. The gastrointestinal absorption of these compounds was determined after intragastric administration. Analogs of Aeg bearing a substituent at the amino or carboxyl functions were absorbed t o a lesser extent than the parent compound. In contrast, the di-and tetra-oligomers of Aeg were more rapidly absorbed. Total absorption of these compounds was observed within 2 h after intragastric administration.