L-CYSTEINE AND GLUTATHIONE METABOLISM ARE IMPAIRED IN PREMATURE-INFANTS DUE TO CYSTATHIONASE DEFICIENCY

There are conflicting reports in the literature as to whether L-cystei ne is an essential amino acid in premature infants as the result of th e absence of hepatic cystathionase activity. To analyze the physiologi cal importance of the cys tathionase deficiency, we studied sulfur ami no acid metabolism in human neonates of different gestational ages. Pl asma cystathionine concentrations are higher in premature infants less than or equal to 32 wk gestation (group 1) than in premature infants of 33-36 wk gestational age (group 2) or in full-term infants (group 3 ), whereas plasma cysteine concentrations are much lower in group 1 an d 2 premature infants than in mature infants. Furthermore, erythrocyte s from group 1 premature infants synthetize glutathione from L-methion ine (a process dependent on the cystathionase pathway) at a much lower rate than do erythrocytes from group 2 premature or full-term infants . Thus, the metabolic flow through the transsulfuration pathway may be insufficient to meet the glutathione and cysteine requirements of ver y premature infants.