Delta-Pyrroline-5-carboxylic Acid Dehydrogenase in Barley, a Proline-accumulating Species

The characteristics of the enzyme Delta(1)-pyrroline-5-carboxylic acid dehydrogenase from etiolated barley (Hordeum distichum) shoots have been examined. The bulk of the enzyme activity was found in the 10,000g pellet fraction, this activity being displayed only after detergent treatment of the suspended pellet. The enzyme was most active at pH 8, and activity was NAD-dependent. Enzyme activity was unaffected by either mannitol or sucrose in the reaction mixture up to a concentration of 0.45 m but was strongly inhibited by Cl(-) and, to a lesser extent, SO(4) (2-). The inhibition attributable to KCl was reversed by increasing the concentration of Delta(1)-pyrroline-5-carboxylic acid in the reaction mixture.