Ketopantoyl lactone and ketopantoic acid reductases. Characterization of the reactions and purification of two forms of ketopantoyl lactone reductase.

Spectral and chromatographic data as well as methods for synthesis of 14C-labeled ketopantoic acid, ketopantoyl lactone, pantoic acid, and pantoyl lactone are presented. The products of ketopantoic acid and ketopantoyl lactone reductases were characterized as pantoic acid and pantoyl lactone, respectively. Unlike pantoyl lactone, ketopantoyl lactone spontaneously hydrolyzes and has a half-life of 2.2 min at pH 7. Purification of ketopantoyl lactone reductase resulted in the separation of two nearly homogeneous forms of the enzyme. Both forms have nearly the same molecular weight (27,000) and exhibit similar kinetic properties. The Michaelis constants of ketopantoyl lactone and NADPH, respectively, are 14 and 62 PM with Form A of the enzyme and 31 and 39 PM with Form B of the enzyme. Each has a molecular activity of about 2,700. A potential function of the enzyme for cell division is discussed.