Figure 3.

Proposed diosgenin biosynthetic pathway. 3-Hydroxy-3-methylglutaryl-CoA is converted to mevalonate by 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) enzyme. This is the major rate limiting step of isoprenoid pathway. Mevalonate is converted to isopentenyl pyrophosphate via series of multiple reactions. Then, diosgenin is produced from squalene by two routes: via cholesterol from lanosterol and via sitosterol from cycloartenol to sterol 3-β-d-glucoside. Finally, the latter is converted to diosgenin by sterol 3-β-glucosyl transferase (STRL) enzyme (dashed lines indicate multiple steps involved in the pathway; arrows indicate the flow of reaction in pathway).