NADPH-dependent conjugated polyketone reductase with broad substrate specificity and strict stereospecificity. Reduces ketopantoyl lactone and isatin. Does not act on menadione, p-nitrobenzaldehyde and pyridine-3-aldehyde. (R)-pantolactone + NADP(+) = 2-dehydropantolactone + H(+) + NADPH (R)-pantolactone + NADP(+) = 2-dehydropantolactone + H(+) + NADPH Inhibited by quercetin. Optimum pH is 7. Optimum temperature is 40 degrees Celsius. Monomer. The N-terminus is blocked. Belongs to the aldo/keto reductase family.