Transamination of L-cysteine sulfinate in the growing rat.

The enzyme activities involved in the transamination of L-cysteine sulfinate (L-alanine 3-sulfinic acid), L-aspartate and L-cysteine were examined in fetal, neonatal and maternal rat liver and placenta. In fetal and neonatal rat liver, aminotransferase activity was most active with L-cysteine sulfinate as a substrate and was also active with L-aspartate, while activity with L-cysteine was very low. The activity of transamination of L-cysteine sulfinate in rat liver developed in parallel with that of L-aspartate and L-cysteine. The aminotransferase activity markedly increased after the 19th day of gestation, reaching the same value as adult liver on the 3rd day after birth. The ratios of transamination of L-cysteine sulfinate to that of L-aspartate and to that of L-cysteine were constant during development. These observations suggest that L-cysteine sulfinate, L-aspartate and L-cysteine are transaminated by the same enzyme in the rat liver during development. Since placental aminotransferase activity was extremely low compared with that of the liver, it was suggested that the placenta did not play an important role in the transamination of these amino acids during pregnancy.