Separation and Preliminary Studies on 2-Ketopantoyl Lactone and 2-Ketopantoic Acid Reductases of Yeast

Two enzymes have been detected and partially purified from yeast. One of them, 2-ketopantoyl lactone reductase, exhibits maximum activity at pH 7.0, converting 1 mole of 2-ketopantoyl lactone to pantoyl lactone for each mole of NADPH oxidized. NADPH and 2-ketopantoyl lactone are the only compounds tested which function well as substrates. The other enzyme, 2-ketopantoic acid reductase, exhibits maximum activity with NADPH and 2-ketopantoic acid at pH 5.0. One mole of pantoic acid is formed for each mole of NADPH oxidized. When tested at 0.1 mm concentration, NADH is a less effective substrate than an equivalent amount of NADPH. With the possible exception of 2-ketopantoyl lactone, none of the other compounds tested functioned well as keto substrates.