Sulfur Amino Acid Metabolism in the Developing Rhesus Monkey Brain: Subcellular Studies of Taurine, Cysteinesulfinic Acid Decarboxylase, γ‐Aminobutyric Acid, and Glutamic Acid Decarboxylase

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Abstract
Taurine, cysteinesulfinic acid decarboxylase (CSAD), glutamate, GABA and glutamic acid decarboxylase (GAD) were measured in subcellular fractions prepared from occipital lobe of fetal and neonatal rhesus monkeys. [35S]Taurine distribution in subcellular fractions was determined after administration to the fetus via the mother, to the neonate via administration to the mother prior to birth and directly to the neonate at various times after birth. CSAD, glutamate, GABA and GAD all were low or unmeasurable in early fetal life and increased during late fetal and early neonatal life to reach values found in the mother. Taurine was present in large amounts in early fetal life and decreased slowly during neonatal life, arriving at amounts found in the mother not until after 150 days of age. Significant amounts of taurine, CSAD, GABA and GAD were associated with nerve ending components with some indication that the proportion of brain taurine found in these organelles increases during development. All subcellular pools of taurine were rapidly labeled by exogenously administered [35S]taurine. The subcellular distribution of all the components measured was compatible with the neurotransmitter or putative neurotransmitter functions of glutamate, GABA and taurine. The large amount of these 3 amino acids exceeds that required for such function. The excess of glutamate and GABA may be used as a source of energy. The function of excess of taurine is still not clear, although circumstantial evidence favors an important role in the development and maturation of the CNS.