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 Optimum pH is 7.5. Optimum temperature is 50 degrees Celsius. Monomer. The N-terminus is blocked. Belongs to the aldo/keto reductase family.