<p>ApbA, the ketopantoate reductase enzyme <db_xref db="EC" dbkey="1.1.1.169"/> of <taxon tax_id="602">Salmonella typhimurium</taxon> is required for the synthesis of thiamine via the alternative pyrimidine biosynthetic pathway [<cite idref="PUB00020970"/>]. Precursors to the pyrimidine moiety of thiamine are synthesized de novo by the purine biosynthetic pathway or the alternative pyrimidine biosynthetic (APB) pathway. The ApbA protein catalyzes the NADPH-specific reduction of ketopantoic acid to pantoic acid. This activity had previously been associated with the pantothenate biosynthetic gene panE [<cite idref="PUB00020974"/>]. ApbA and PanE are allelic [<cite idref="PUB00020974"/>].</p>