PFAS (phosphoribosylformylglycinamidine synthase) is an ATP-dependent enzyme catalyzing a critical step in de novo purine biosynthesis. It converts formylglycinamide ribonucleotide (FGAR) and glutamine to formylglycinamidine ribonucleotide (FGAM), facilitating the synthesis of AMP, GMP, IMP, and XMP nucleotides in the cytoplasm and cytosol. This enzyme is essential for generating purine ribonucleoside monophosphates required for DNA and RNA synthesis. Note: The PubMed abstracts provided discuss per- and polyfluoroalkyl substances (environmental contaminants), which share the acronym PFAS but are entirely unrelated to the phosphoribosylformylglycinamidine synthase gene. No abstracts addressing the gene function, mechanism, disease relevance, or clinical significance of the PFAS enzyme were available for citation. The functional information above derives solely from the provided UniProt and Gene Ontology annotations, which are not peer-reviewed literature sources. To provide a comprehensive gene function summary with proper PubMed citations would require abstracts specifically investigating phosphoribosylformylglycinamidine synthase function, mutations, or disease associations.