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Of The amino acids and derivatives, N‐acetyl‐L‐aspartic acid is present in a uniquely high level (5–6 μmol/g) in the brain of mammals after myelination has occurred. Much lower levels (0·06–0·17 μmol/g) are found prior to this stage of brain development (Tallan, 1957). In non‐nervous tissues, on the other hand, only trace amounts of this acetyl amino acid are present (Tallan, Moore and Stein, 1956). N‐acetyl aspartic acid serves as an excellent source of acetyl groups for lipogenesis in the developing rat brain (D'Adamo and Yatsu, 1966; Dadamo, Gidez and Yatsu, 1968). Non‐nervous tissues such as kidney and mammary gland also rapidly metabolize the acetyl amino acid, the former tissue converting the acetyl group primarily to CO2 and the latter to fatty acids (Benuck and D'Adamo, 1968). An enzyme with a high specificity for N‐acetyl‐L‐aspartic acid initially termed aminoacylase II, was originally isolated from hog kidney by Birnbaumet al. (1952). Since the physiological role of the substrate is not known, it was of interest to study the occurrence of this enzyme, N‐acetyl‐L‐aspartate amidohydrolase (EC 3.5.1.15), in developing tissues of the rat.

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Abstract— The enzyme in rat brain responsible for the de‐acetylation of N‐acetyl‐aspartic acid has been partially purified. In contrast to the enzyme from hog kidney which is stable at 70°C, it rapidly denatures above 57°C. The rat brain enzyme has the same Km for its substrate and the same solubility in ammonium sulphate solution as the hog kidney enzyme. Results of migration on starch gel electro‐phoreses and isoelectric focusing indicate a pI for the amidohydrolase of 5.1. A variety of potential substrates, modulators, and inhibitors have been examined.

~~-2-Deuteriolactic acid has been prepared with incorporation of deuterium in approximately 75 atom per cent excess by concurrent hydrolysis and decarboxylation of bromomethylmalonic acid in refluxing deuterium oxide or by prior decarboxylation of the deuterium exchanged solid bromo di-acid to 2-deuterio-2-bromopropionic acid followed by hydrolysis with zinc carbonate.

Radioactive acetyl groups and lipids are produced from dl‐[5‐14C]glutamate. Degradation studies indicate that approximately 90 per cent of the radioactivity is localized in the original carboxyl groups of the two carbon unit. Since these results are shown not to be due to a 14CO2 fixation, it is concluded that the oxoglutarate shunt as an acetyl group transport system is functional in brain. The highest ratio of fatty’acid activity/CO2 activity in this pathway is found in the newborn rat brain and steadily decreases with development. This pattern is observed with incubations of brain slices with labelled glutamate or citrate and is similar to the changes observed in the activity of the citrate cleavage enzyme with brain maturation. In contrast to the previous studies with liver preparations, the conversion of [2‐14C]‐ and [5‐14C]glutamate to fatty acids is relatively small. This is particularly true during the period of maximal lipid synthesis.