40] Ketopantoyl lactone reductases

Abstract

This chapter presents an overview of ketopantoyl lactone reductases. Fungi are reported to metabolize ketopantoyl lactone to a nonracemic mixture of DL-pantoyl lactone. However, the formation of D-(-)-pantoyl lactone may relate to coenzyme A metabolism, because on hydrolysis, it forms o-(+)-pantoic acid, a precursor of coenzyme A. The purification and properties of two forms of ketopantoyl lactone reductase, which convert ketopantoyl lactone to D-(-)-pantoyl lactone, are described in the chapter. Ketopantoyl lactone reductase activity is assayed by the spectrophotometric measurement of ketopantoyl lactone-dependent oxidation of nicotinamide adenine dinucleotide phosphate (NADPH). The assay for ketopantoyl lactone reductase in crude extracts is complicated by the occurrence of NADPH oxidase and ketopantoic acid reductase in the extracts. Ketopantoic acid reductase is detected in this assay system, because ketopantoic acid is formed during the assay by the rapid spontaneous hydrolysis of ketopantoyl lactone. The chapter also describes the growth and harvest of yeast.