Effect of the superoxide anion (O2-) on Na+-dependent amino acid transport

Superoxide anion (O2-) generated either by the autoxidation of dihydroxyfumaric acid (DHF) or enzymatically by the xanthine-xanthine oxidase system inhibited the uptake of 2-aminoisobutyric acid (AIB) in thymocytes. The transport of this non-metabolizable amino acid in thymocytes is mediated by a Na+-dependent mechanism. Inhibition of this transport system by O2- was similar to that observed when radiosensitive lymphocytes are subjected to ionizing radiation. As in irradiated thymocytes, O2- generation affected primarily the maximal rate of uptake of the amino acid (i.e. Vmax). No change was observed in the apparent affinity of the amino acid for its carrier (i.e. Km) or the efflux rate of the amino acid. The data suggests that the superoxide anion may be one of the major species responsible for the observed radiation damage to radiosensitive lymphoid cells.