Component of a complex that catalyzes the reversible migration of the omega amino group of D-ornithine to C-4 to form (2R,4S)-2,4-diaminopentanoic acid. The role of OraS remains obscure; however, it seems to be required for a correct folding of the OraE subunit. The complex is active only on D-ornithine and 2,4-diaminopentanoic acid and not active on L-ornithine, L-beta-lysine, L-alpha-lysine or D-alpha-lysine. D-ornithine = (2R,4S)-2,4-diaminopentanoate Increased activity in the presence of dithiothreitol (DTT) in vitro. Inhibited by 1 mM potassium phosphate and potassium chloride. Inhibited by L-alpha-ornithine, D,L-alpha-lysine, L-beta-lysine (50%-60%), L-alpha-lysine (26%) and by delta-amino-n-valeric acid to a lesser extent. Significant decrease in activity is observed in the presence of 0.2 mM p-chloromercuribenzoate, N-ethylmaleimide and also by 2 mM iodoacetate to a lesser extent but not inhibited by arsenite. Optimum pH is 9.0 or between 8.5-8.7 (with Tris-HCl buffer). Half-maximal activity is observed at pH 7.4 and 9.7. Optimum temperature is 37 degrees Celsius for native enzyme. Displays half-maximal activity at 23 degrees Celsius and 49 degrees Celsius. Rapidly inactivated at temperatures above 45 degrees Celsius. Loses more than 35% and 30% of its activity when stored at -20 degrees Celsius for 1 month and at 4 degrees Celsius for 48 hours, respectively. Heterotetramer of 2 alpha (OraS) and 2 beta (OraE) subunits.