Ornithine transaminase in Neurospora and its relation to the biosynthesis of proline.

The mould Neurospora crassa is normally able to interconvert proline and ornithine, since either proline or ornithine will satisfy the growth requirement of certain mutant strains (Srb, Fincham & Bonner, 1950). Another mutant requires proline specifically, while numerous other strains, representing at least four different genetic loci, respond to ornithine but not to proline (Srb & Horowitz, 1944). A knowledge of the enzymic mechanisms involved in the interconversion of these two amino-acids is clearly necessary for a fuller understanding of the effects of the mutations concerned. The present study was suggested by the possibility that one step in the conversion of ornithine to proline might be the transfer of one of the amino groups of ornithine to an amino acceptor such as c-ketoglutaric acid. Quastel & Witty (1951) have reported the presence of an ornithine transaminase in animal tissues, and the author (Fincham, 1951) found that ornithine was one of a number of aminoacids to be transdeaminated by Neurospora extracts. This paper deals in more detail with the Neurospora enzyme and with the nature of the products of the reaction.