This is a family of 2-dehydropantoate 2-reductases also known as ketopantoate reductases, EC:18.104.22.168. The reaction catalyzed by this enzyme is: (R)-pantoate + NADP(+) <=> 2-dehydropantoate + NADPH. AbpA catalyzes the NADPH reduction of ketopantoic acid to pantoic acid in the alternative pyrimidine biosynthetic (APB) pathway. ApbA and PanE are allelic. ApbA, the ketopantoate reductase enzyme is required for the synthesis of thiamine via the APB biosynthetic pathway.