COPPER-AMINO ACID COMPLEXES ARE PARTIALLY PROTECTED AGAINST INHIBITORY EFFECTS OF L-CYSTEINE AND L-ASCORBIC-ACID ON COPPER ABSORPTION IN CHICKS

Chick experiments were conducted to investigate whether two new Cu-amino acid complexes, Cu-methionine (Cu-Met) and Cu-lysine (Cu-Lys), would differ from a standard Cu source (analytical-grade CuSO4) in their reaction to the inhibitory dietary effects of physiologic doses of L-cysteine (4000 mg/kg diet) or L-ascorbate (1000 mg/kg diet) on Cu absorption. Whether absorbed actively (as evaluated by a bile Cu assay at low Cu doses) or passively (as evaluated by a liver Cu assay at high Cu doses), cysteine inhibited Cu absorption more than did ascorbate. In addition, the inhibitory effects of cysteine and ascorbate were not additive, but they enhanced the inhibitory effect of Zn when evaluated at low Cu doses. Ascorbate inhibited Cu utilization from CuSO4 to 58.0% of the unsupplemented reference group at low Cu doses, which was greater (P < 0.05) than the inhibitory effect of ascorbate of Cu-Lys (78.7%) or Cu-Met (89.1%). Cysteine inhibited Cu utilization from CuSO4, Cu-Lys and Cu-Met at low Cu dose levels to 49.1, 44.1 and 50.2%, respectively, of unsupplemented reference groups of each source. These values were not different from each other. On the other hand, cysteine inhibited Cu utilization from CuSO4 to 8.5% of the unsupplemented reference group at high Cu doses, which was greater (P < 0.05) than the inhibitory effect on Cu-Lys (29.5%) or Cu-Met (39.9%). Ascorbate reduced Cu utilization from CuSO4, Cu-Lys and Cu-Met at high Cu doses to 72.8, 63.7 and 68.3%, respectively, of unsupplemented control groups of each source.