The Enzymatic Synthesis of N-Acetyl-l-aspartic Acid by a Water-insoluble Preparation of a Cat Brain Acetone Powder

An acetone powder of cat brain catalyzed the synthesis of two radioactive products when incubated with L-aspartate-14C and acetyl coenzyme A. The products were identified as Nacetyl-aspartic acid and citric acid.A water extract of the powder contained the system that produced citrate-14C, while the residue contained the aspartate N-acetyltransferase activity.The soluble system rather than the residue exhibited characteristics previously reported for a soluble aspartate Nacetyltransferase preparation of rat brain; hence, it is suggested that previous investigators were not measuring true L-aspartate N-acetyltransferase activity.N-;-r,-asl?artic acid is a charajct8erintic component of the amino acid pool of the nervous tissue of vertebrates, whereas only trace amounts are found in other tissues and organs (1, 2).This paper describes an enzyme preparation from the brain of rats that unequivocally synthcsizcs N-acetyl-L-aspartic acid from L-aspartic acid-% (uniformly labeled) and acetyl coenzyme A.Previous evidence that preparations in vitro of nervous tissue synthesize NAA from simple precursors is conflicting.Tallan (2) was not able to show synthesis in brain extracts or homogenates.Goldstein (3) reported the isolation from a rat brain homogenate of a water-soluble enzyme that converted acetyl CoA and L-aspartate to N-acetyl-L-aspartic acid.Jacobson (4) reported the incorporation of radioactivity into N-acetyl-L-as: partic acid when minced mouse brain was incubated with either L-aapartatc-'4C or sodium a&al+%.IIe could not show these results with a cell-free homogenate.Gebhard and Veldstra (5), with the use of different analytic techniques, were not able to repeat the positive findings of Goldstein or Jacobson.