ON THE GLUTAMATE-PROLINE-ORNITHINE INTERRELATION IN NEUROSPORA CRASSA

Abstract

In N. crassa proline is mainly synthe-sized from glutamate via glutamic y-semialdehyde and /}* -pyrroline-5-carboxylate. Another route to proline proceeds from exogenous ornithine via glutamic V -semialdehyde and ^1 -pyrroline-5-carboxylate. Evidence for the sequence glutamate-glutamic Y -semialdehyde-ornithine has been obtained, but the quantitative significance of this path is unknown. Neurospora mutants responding alternatively to proline, ornithine, or glutamic y -semialdehyde appear to be blocked between glutamate and glutamic y -semialdehyde as proline precursor. Such mutants accumulate keto acids, among which a-ketoisovaleric acid has been identified. A mutant responding to proline but not to glutamic ?-semialdehyde presumably is blocked in the conversion of the semialdehyde to proline. Evidence has been presented which indicates that certain of the metabolites involved in the glutamate-proline-ornithine interrelation may be "channeled" as a result of the spatial organization of relevant enzyme systems. The possibility has been considered that certain Neurospora mutants responding to ornithine but not to proline may be blocked through a disturbance in enzyme organization. The glutamate-proline-ornithine interrelation in Neurospora is strikingly similar to that in mammals but differs from that in E. coli.