Catalyzes the conversion of L-ornithine into L-proline with release of ammonia. Is involved in the utilization of nopaline, a catabolic pathway that proceeds through L-arginine and L-ornithine to L-proline. Nopaline is a predominant opine in plant cells transformed with Ti plasmid pTiC58. L-ornithine = L-proline + NH4(+) Is subject to substrate inhibition. Is regulated by L-arginine, which stimulates enzymatic activity at 0.1-1 mM while inhibits activity at higher concentrations, and has pronounced effects on the optima for pH and temperature and on the Km for L-ornithine. Is not inhibited by L-proline. Optimum pH is 8.0-9.5 in the presence of L-arginine, and 8.5-9.0 in the presence of 1 mM L-arginine. Optimum temperature is 25-35 degrees Celsius in the presence of L-arginine, and 38-42 degrees Celsius in the presence of 1 mM L-arginine. Amino-acid biosynthesis; L-proline biosynthesis; L-proline from L-ornithine: step 1/1. Is induced by nopaline. Belongs to the ornithine cyclodeaminase/mu-crystallin family.