ID   2.5.1.21
DE   Squalene synthase.
AN   Farnesyl-diphosphate farnesyltransferase.
AN   Farnesyltransferase.
AN   Presqualene synthase.
AN   Presqualene-diphosphate synthase.
AN   Squalene synthetase.
CA   (1) 2 farnesyl diphosphate = diphosphate + presqualene diphosphate.
CA   (2) Presqualene diphosphate + NAD(P)H = squalene + diphosphate +
CA   NAD(P)(+).
CF   Manganese or magnesium.
CC   -!- This microsomal enzyme catalyzes the first committed step in the
CC       biosynthesis of sterols.
CC   -!- In the absence of NAD(P)H, presqualene diphosphate (PSPP) is
CC       accumulated.
CC   -!- When NAD(P)H is present, presqualene diphosphate does not dissociate
CC       from the enzyme during the synthesis of squalene from farnesyl
CC       diphosphate (FPP).
CC   -!- High concentrations of FPP inhibit the production of squalene but not
CC       of PSPP.
PR   PROSITE; PDOC00802;
DR   P53799, FDFT_ARATH ;  Q752X9, FDFT_ASHGO ;  Q32KR6, FDFT_BOVIN ;
DR   P78589, FDFT_CANAX ;  Q9HGZ6, FDFT_CANGA ;  O74165, FDFT_CYBJA ;
DR   Q54DR1, FDFT_DICDI ;  P37268, FDFT_HUMAN ;  P53798, FDFT_MOUSE ;
DR   Q7S4Z6, FDFT_NEUCR ;  P53800, FDFT_NICBE ;  Q5R6U3, FDFT_PONAB ;
DR   Q02769, FDFT_RAT   ;  P36596, FDFT_SCHPO ;  Q92459, FDFT_USTMA ;
DR   Q9Y753, FDFT_YARLI ;  P29704, FDFT_YEAST ;
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