Purine nucleoside enzyme that catalyzes the phosphorolysis of adenosine, guanosine and inosine nucleosides, yielding D-ribose 1-phosphate and the respective free bases, adenine, guanine and hypoxanthine (PubMed:31978345). Also catalyzes the phosphorolysis of S-methyl-5'-thioadenosine into adenine and S-methyl-5-thio-alpha-D-ribose 1-phosphate (PubMed:31978345). Also has adenosine deaminase activity (PubMed:31978345). Acts as a regulator of innate immunity in macrophages by modulating the purine nucleotide metabolism, thereby regulating the metabolic function and bioenergetic state of macrophages (PubMed:31978345). Enables a purine nucleotide cycle between adenosine and inosine monophosphate and adenylosuccinate that prevents cytoplasmic acidification and balances the cytoplasmic-mitochondrial redox interface (PubMed:31978345). The purine nucleotide cycle consumes aspartate and releases fumarate in a manner involving fatty acid oxidation and ATP-citrate lyase activity (PubMed:31978345). Participates in pattern recognition receptor (PRR)-induced cytokines in macrophages: associates with the NOD2-signaling complex and promotes optimal NOD2-induced signaling, cytokine secretion and bacterial clearance (PubMed:28593945, PubMed:31875558). Localizes to the endoplasmic reticulum upon PRR stimulation of macrophages and associates with endoplasmic reticulum-stress sensors, promoting the endoplasmic reticulum unfolded protein response (UPR) (PubMed:31875558). Does not show laccase activity (PubMed:27959965, PubMed:31978345). adenosine + phosphate = adenine + alpha-D-ribose 1-phosphate inosine + phosphate = alpha-D-ribose 1-phosphate + hypoxanthine guanosine + phosphate = alpha-D-ribose 1-phosphate + guanine phosphate + S-methyl-5'-thioadenosine = adenine + S-methyl-5-thio-alpha-D-ribose 1-phosphate adenosine + H(+) + H2O = inosine + NH4(+) Interacts with FASN (PubMed:27478939). Interacts with SDHA (PubMed:28593945). Interacts with ATF6, EIF2AK3 and ERN1 (PubMed:31875558). Upon stimulation of the pattern-recognition receptor (PRR) NOD2, localizes to the endoplasmic reticulum. Ubiquitously expressed, with higher expression levels in immune-related tissues such as lymph nodes and spleen (PubMed:27959965). Expressed in both intestinal and peripheral myeloid-derived cells (PubMed:28593945). Up-regulated by phorbol 12-myristate 13-acetate (PMA) (PubMed:27959965). Down-regulated by PPAR ligands (PubMed:27959965). Up-regulated upon pattern recognition receptor (PRR) stimulation (PubMed:28593945). Phosphorylated on tyrosine residues. The disease is caused by variants affecting the gene represented in this entry. Belongs to the purine nucleoside phosphorylase YfiH/LACC1 family.