018 CHAPTER 26 Lipids
The mechanism for converting mevalonic acid into mevalonyl phosphate is essen-
tially an reaction with an adenosyl pyrophosphate leaving group (Section 27.3). A
second reaction converts mevalonyl phosphate to mevalonyl pyrophosphate. ATP
is an excellent phosphorylating reagent for nucleophiles because its phosphoanhydride
bonds are easily broken. The reason that phosphoanhydride bonds are so easily broken
is discussed in Section 27.4.SN 2SN 2O−OO OSCoA−OOH OOH++++acetyl-CoA malonyl-CoA acetoacetyl-CoAhydroxymethylglutaryl-CoAClaisen
condensationbiosynthesis of isopentenyl pyrophosphate1.2.CoASH CO 2H 2 OADP ATP 2 NADP+ 2 NADPHmevalonic acidmevalonyl phosphateOOHCOO−CO 2OH O
PO−O−SCoAO OSCoAO OSCoASCoACOO−COO−+ CoASH++CO 2ADPADPATPATPO O− HOmevalonyl pyrophosphate isopentenyl pyrophosphateOOHOPO−OPO−O O O−OPO−OPO−O−OPO−
COO−OHOH
COO−−OOOPO−+mevalonic acidadenosineATPOOPO−OOPO−O ++−mevalonyl pyrophosphate−O−OADPOHOOPO–OOHOOPO−OPO−O−OOPO−OOPO−OO
PO−OO
PO−adenosine−OADPOOPO−OOPO−adenosineOO
PO−adenosineCOO−COO−+H+