Ddo^−/− mice display elevated d-aspartate levels. A, HPLC amino acid analysis of 4-week-old kidney d-aspartate (Ddo^+/+ vs Ddo^+/−, p = 0.021; Ddo^+/− vs Ddo^−/−, p = 0.008). B, Four-month-old kidney d-aspartate (Ddo^+/+ vs Ddo^−/−; p = 0.004). C, Four-month-old brain d-aspartate (Ddo^+/+ vs Ddo^−/−; p = 0.0009). D, Four-month-old adrenal d-aspartate (Ddo^+/+ vs Ddo^−/−; p = 0.00001). E, Four-month-old ovarian d-aspartate (Ddo^+/+ vs Ddo^−/−; p = 0.000004). F, Four-month-old testicular d-aspartate (Ddo^+/+ vs Ddo^−/−; p = 0.0001) and l-aspartate (Ddo^+/+ vs Ddo^−/−; p = 0.013). *p < 0.05; **p < 0.01; ***p < 0.001; comparison with two-tailed Student’s t test; data are expressed as mean ± SEM.