α-Aminoisobutyric acid is actively transported into yeast cells by the general amino acid transport system. The system exhibits a Km for α-aminoisobutyric acid of 270 μM, a Vmax of 24 nmol/min per mg cells (dry weight), and a pH optimum of 4.1-4.3. α-Aminoisobutyric acid is also transported by a minor system(s) with a Vmax of 1.7 nmol/min per mg cells. Transport occurs against a concentration gradient with the concentration ratio reaching over 1000:1 (in/out). The α-aminoisobutyric acid is not significantly metabolized or incorporated into protein after an 18 h incubation. α-Aminoisobutyric acid inhibits cell growth when a poor nitrogen source such as proline is provided but not with good nitrogen sources such as NH4+. During nitrogen starvation α-aminoisobutric acid strongly inhibits the synthesis of the nitrogen catabolite repression sensitive enzyme, asparaginase II. Studies with a mutant yeast strain (GDH-CR) suggest that α-aminoisobutyric acid inhibition of asparaginase II synthesis occurs because α-aminoisobutyric acid is an effective inhibitor of protein synthesis in nitrogen starved cells.
Bibliographical noteFunding Information:
Supported by USPHS NIH Grant GM-22374 and by a University of Minnesota Graduate School Grant.
- (S. cerevisiae)
- Amino acid transport
- α-Aminoisobutyric acid