Pantothenic acid and -alanine are metabolic intermediates in coenzyme A biosynthesis. Using a functional screen in the yeast Saccharomyces cerevisiae, a putative amine oxidase, encoded by FMS1, was found to be ratelimiting for -alanine and pantothenic acid biosynthesis. Overexpression of FMS1 caused excess pantothenic acid to be excreted into the medium, whereas deletion mutants required -alanine or pantothenic acid for growth. Furthermore, yeast genes ECM31 and YIL145c, which both have structural homology to genes of the bacterial pantothenic acid pathway, were also required for pantothenic acid biosynthesis. The homology of FMS1 to FAD-containing amine oxidases and its role in -alanine biosynthesis suggested that its substrates are polyamines. Indeed, we found that all the enzymes of the polyamine pathway in yeast are necessary for -alanine biosynthesis; spe1⌬ , spe2⌬ , spe3⌬ , and spe4⌬ are all -alanine auxotrophs. Thus, contrary to previous reports, yeast is naturally capable of pantothenic acid biosynthesis, and the -alanine is derived from methionine via a pathway involving spermine. These findings should facilitate the identification of further enzymes and biochemical pathways involved in polyamine degradation and pantothenic acid biosynthesis in S. cerevisiae and raise questions about these pathways in other organisms.Pantothenic acid (vitamin B 5 ) is a metabolic precursor to coenzyme A (CoA) and acyl carrier protein, which are cofactors required by a large number of metabolic enzymes. Biosynthesis of pantothenic acid occurs in microbes and plants only, whereas animals obtain it in their diet. In bacteria, it is synthesized by the condensation of pantoate, derived from 2-oxoisovalerate, an intermediate in valine biosynthesis, and -alanine, produced by the decarboxylation of L-aspartate (1, 2). In Escherichia coli, four genes, panB, panC, panD, and panE, encode the four enzymes required for pantothenic acid biosynthesis, as illustrated in Fig.
