The enzyme ent-kaurene synthase (EC 4.2.3.19) catalyzes the chemical reaction

ent-copalyl diphosphate ${\displaystyle \rightleftharpoons }$ ent-kaurene + diphosphate

This enzyme belongs to the family of lyases, specifically those carbon-oxygen lyases acting on phosphates. The systematic name of this enzyme class is ent-copalyl-diphosphate diphosphate-lyase (cyclizing, ent-kaurene-forming). Other names in common use include ent-kaurene synthase B, ent-kaurene synthetase B, ent-copalyl-diphosphate diphosphate-lyase, and (cyclizing). This enzyme participates in diterpenoid biosynthesis.

In Stevia spp., ent-kaurene synthase is a required part of the biosynthesis of steviol.^[1][2] Hajihashemi et al., 2013 find that it is involved in the drought stress response and – because it mimics drought stress – paclobutrazol toxicity.^[1][2] Both inhbit transcription of steviol glycoside synthesis genes including ent-kaurene synthase.^[1][2] This is believed to reduce steviol content in the final plant product.^[1][2]

• Fall RR, West CA (1971). "Purification and properties of kaurene synthetase from Fusarium moniliforme". J. Biol. Chem. 246 (22): 6913–28. PMID 4331199.
• Yamaguchi S, Saito T, Abe H, Yamane H, Murofushi N, Kamiya Y (1996). "Molecular cloning and characterization of a cDNA encoding the gibberellin biosynthetic enzyme ent-kaurene synthase B from pumpkin (Cucurbita maxima L.)". Plant J. 10 (2): 203–13. doi:10.1046/j.1365-313X.1996.10020203.x. PMID 8771778.
• Kawaide H, Imai R, Sassa T, Kamiya Y (1997). "Ent-kaurene synthase from the fungus Phaeosphaeria sp. L487. cDNA isolation, characterization, and bacterial expression of a bifunctional diterpene cyclase in fungal gibberellin biosynthesis". J. Biol. Chem. 272 (35): 21706–12. doi:10.1074/jbc.272.35.21706. PMID 9268298.
• W, Sassa T; Kawaide, H; Ishizaki, A; Shinoda, S; Otsuka, M; Mitsuhashi, W; Sassa, T (2000). "Cloning of a full-length cDNA encoding ent-kaurene synthase from Gibberella fujikuroi: functional analysis of a bifunctional diterpene cyclase". Biosci. Biotechnol. Biochem. 64 (3): 660–4. doi:10.1271/bbb.64.660. PMID 10803977.