Pyrroline-5-carboxylate reductase and

Vansuyt, G., J.C. Vallee, and J. Prevost Pyrroline-5-carboxylate reductase and prohne dehydrogenase in Nicotiana tabacum var. Xanthi NC as a function of its development Physiol. Veg. 17 (1979) 95-105. 

Samuels, S.E., K.S. Acton, and R.O. Ball, 1989. Pyrroline-5-carboxylate reductase and proline oxidase activity in the neonatal pig. J. Nutr. 119, 1999-2004. 

Noguchi, M., A. Koiwai, and E. Tamaki Studies on nitrogen metabolism in tobacco plants. Part VII. 5-Pyrroline-5-carboxylate reductase from tobacco leaves Agr. Biol. Chem. (Tokyo) 30 (1966) 452-456. 

A -Pyrroline-5-carboxylate reductase catalyzes the reduction of this compound to proline. In the rat liver enzyme DPNH and, less effectively, TPNH serve as hydrogen donors 115,120,123). In the Neurospora enzyme TPNH is sixteen times as effective as DPNH 124). A -Pyrroline-S-car-boxylate reductase has been observed in various mammalian tissues 120, 123) and in a variety of microorganisms 116, 123-126). The enzyme has been purified about thirtyfold, from Neurospora 126) and about eightyfold in the writer s laboratory from animal tissue 126). The enzyme is active on a number of A -pyrroline derivatives. The optimum activity of the liver and Neurospora enzymes is at about pH 7.0. The reductase is an SH enzyme and it is strongly inhibited by the usual SH reagents. Estimation of the kinetic constants of the liver enzyme yielded X values of 2.0 X 11" M for pyrroline-5-carboi late and 2.5 X 10 M for DPNH. 

With the exception of the last enzyme in the pathway, pyrroline-5-carboxyl-ate reductase (13) (e.g., Krueger et al, 1986), little is known about the enzymes associated with proline biosynthesis in higher plants. All of the detectable activity of the reductase was found in pea chloroplasts (Rayapati and Stewart,... 

Fig. 12. Possible pathways of citniUine metabolism. Numbered enzymes are (1) ornithine trans-carbamoylase, (2) citrulline hydrolase (EC 3.5.1.20), (3) omithinerS-oxoglutatate aminotransferase, (4) carbamate phosphotransferase, (5) glutamine synthetase, (7) pyrroline-S-carboxylate reductase, (8) proline dehydrogenase, (9) pyiToline-S-carboxylate NAD(P) oxidoreductase, (10) glutamate dehydrogenase, (11) aminotransferase, (12) argininosuccinate synthetase, (13) arginino-succinate lyase, (14) fiimaiase, (IS) aspartate aminotransferase, (16) aiginase, (17) urease, and (18) ornithine cyclodeaminase.

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