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Title: KINETICS AND SPECIFICITY OF A H*/AMINO ACID TRANSPORTER FROM ARABIDOPSIS THALIANA

Author
item BOORER, KATHRYN - UCLA SCHOOL OF MEDICINE
item FROMMER, WOLF - GENBIOLOGISCHE BERLIN
item BUSH, DANIEL
item KREMAN, MICHAEL - UCLA SCHOOL OF MEDICINE
item LOO, DONALD - UCLA SCHOOL OF MEDCINE
item WRIGHT, ERNEST - UCLA SCHOOL OF MEDICINE

Submitted to: The Plant Cell
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Plant leaves capture light energy from the sun and transform that energy into a useful form in the process called photosynthesis. One important use of that energy is in the reductive assimilation of inorganic nitrogen into amino acids. Generally, most amino acids thus formed in the leaf are transported to plant tissues of agricultural significance (fruit, grain, and tubers) that are dependent upon imported sugars and amino acids for normal growth and development. Alterations in the transport process are known to significantly affect crop productivity. The work reported here describes the molecular description of the transport properties of a plant amino acid carrier. These results provide insight into the structure and function of this carrier, and open the door for manipulating crop productivity and nutritional quality.

Technical Abstract: The amino acid transporter NAT2/AAP1 recently cloned from Arabidopsis was expressed in Xenopus oocytes and its biophysical and kinetic properties were measured with electrophysiological, radiotracer flux, and electron microscopic methods. Uptake of alanine was pH-dependent, increasing from 14 pmol/oocyte/h at 0.032 micromole protons to 370 pmol/oocyte/h at 10 micromole protons. Flux was electrogenic as demonstrated by uptake dependent depolarization of the oocyte membrane potential and net inward positive currents. The maximal current for alanine, proline, glutamine, histidine, and glutamate was voltage and delta pH-dependent. Proton flux was also voltage and delta pH-dependent. The kinetics for proton and amino acid flux suggested the porter functions via a simultaneous binding mechanism. The stoichiometry was 1:1, with evidence of multiple binding sites for both protons and amino acids. The density of particles on the protoplasmic face of the oocyte and current of the carrier corresponds to a turnover number of 300 to 800 molecules per porter per second.