hydroxymethylbilane synthase activity https://github.com/geneontology/go-ontology/issues/30193 (4-(2-carboxyethyl)-3-(carboxymethyl)pyrrol-2-yl)methyltransferase (hydrolyzing) activity GO:0004418 MetaCyc:OHMETHYLBILANESYN-RXN porphobilinogen:(4-[2-carboxyethyl]-3-[carboxymethyl]pyrrol-2-yl)methyltransferase (hydrolysing) Catalysis of the reaction: H2O + 4 porphobilinogen = hydroxymethylbilane + 4 NH4. HMB-synthase activity pre-uroporphyrinogen synthase activity (4-[2-carboxyethyl]-3-[carboxymethyl]pyrrol-2-yl)methyltransferase (hydrolysing) porphobilinogen deaminase activity molecular_function KEGG_REACTION:R00084 uroporphyrinogen I synthetase activity EC:2.5.1.61 Reactome:R-HSA-189406 uroporphyrinogen synthase activity uroporphyrinogen synthetase activity porphobilinogen ammonia-lyase (polymerizing) uroporphyrinogen I synthase activity RHEA:13185 transferase activity, transferring alkyl or aryl (other than methyl) groups