Functional characterization of the chicken cationic amino acid transporter-2 isoforms

Utilization of lysine and arginine by mammalian skeletal muscle is due in large part to the system y+ cationic amino acid transporters (CAT), particularly CAT-2A. The chicken CAT-2 (cCAT-2) gene is alternatively spliced to produce three isoforms (cCAT-2A/B/C). Chicken (Gallus gallus) CAT-2 isoforms were transiently and stably expressed in mammalian cell lines to determine cCAT-2 isoform cellular localization and transport properties. The cCAT-2A protein localized to the plasma membrane and the cCAT-2B protein localized to the cytoplasm juxtaposed to the plasma membrane. The cCAT-2C protein localized non-specifically throughout the cytoplasm. The cCAT-2A protein exhibited saturable transport. The Kt of cCAT-2A for lysine using transient transfection was 2.6 mM and the Vmax was 11.9 pmol/mg protein/min. The Kt of cCAT-2A for lysine using stable transfection was 7.9 mM and the Vmax was 12.8 pmol/mg protein/min. Transient and stable transfections of cCAT-2B or cCAT-2C resulted in no lysine or arginine transport. These data indicate that cCAT-2A is a low affinity, high velocity transporter for lysine and arginine and is the cCAT-2 isoform responsible for lysine and arginine transport in avian skeletal muscle.