Observations on the Conversion of N-Acetylglutamate to Proline in Extracts of Escherichia coli
Donald E. Reed 1 and Lewis N. Lukens 1
From the
1 From the Department of Biochemistry, Yale University, New Haven, Connecticut 06520
An extract of Escherichia coli was found capable of synthesizing proline from N-acetylglutamate. This synthesis was shown to proceed by transformation of the 5 carbon skeleton of acetylglutamate into ornithine by way of the familiar reactions of arginine biosynthesis. This ornithine then undergoes a transamination of its 
-amino group with 
-ketoglutarate, yielding 
'-pyrroline-5-carboxylic acid. The synthesis of the latter compound from acetylglutamate requires both an adenosine triphosphate- and a reduced triphosphopyridine nucleotide-generating system and is stimulated by l-glutamate.
Evidence is presented, however, that the synthesis of proline in vivo does not proceed by this pathway. (a) Exogenous acetylglutamate is incorporated preferentially into arginine, rather than into proline, when compared with exogenous glutamate. (b) Cells grown in the presence of arginine yield extracts devoid of activity for synthesizing proline from acetylglutamate, yet such cells do not require exogenous proline for growth. (c) A proline auxotroph, strain 55–25, blocked between glutamate and '-pyrroline-5-carboxylic acid does not appear to be blocked either between glutamate and ornithine or between ornithine and '-pyrroline-5-carboxylic acid. (d) Proline does not inhibit the transamination of ornithine to yield '-pyrroline-5-carboxylic acid.
Submitted on July 19, 1965
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