Isoprenyl pyrophosphate synthases (IPPSs) are responsible for the synthesis of linear isoprenyl pyrophosphates. They can be classified as cis- or trans-isoprenyl pyrophosphate synthases according to the stereochemical outcome of their products. All-trans C[[10]] geranyl pyrophosphate (GPP) and C[[15]] farnesyl pyrophosphate (FPP) are synthesized by trans-type geranyl pyrophosphate synthase and farnesyl pyrophosphate synthase, respectively. Starting from FPP, a variety of different chain-length all-trans-isoprenyl pyrophosphates and trans,cis-isoprenyl pyrophosphates are generated by the corresponding trans-IPPSs or cis-IPPSs. While short-chain (C15) and medium-chain (C50-55) cis-prenyltransferase complexes are homodimeric, long-chain (C70-120) cis-prenyltransferases are formed by a heteromeric subunit assembly of unknown stoichiometry. (Adapted from PMID:12135472, PMID:26216239, PMID:33077723.)