Dimethylallyl pyrophosphate conversion

The conversion of isopentenyl diphosphate (IPP) to terpenoids begins with its isomerization to dimethylallyl diphosphate, abbreviated DMAPP and formerly called dimethylallyl pyrophosphate. These two C5 building blocks then combine to give the C10 unit geranyl diphosphate (GPP). The corresponding alcohol, geraniol, is itself a fragrant terpenoid that occurs in rose oil. 

The conversion of mevalonate to isopentenyl pyrophosphate and dimethylallyl pyrophosphate. Mevalonate is converted to isopentenyl pyrophosphate in three steps. Each of these steps requires one ATP... 

The conversion of isopentenyl pyrophosphate and dimethylallyl pyrophosphate to geranyl pyrophosphate. 

Conversion of Acetyl Coenzyme A to Isopentenyl Pyrophosphate Section 28.2 Figure 28.1 Conversion of Isopentenyl Pyrophosphate and Dimethylallyl Pyrophosphate to Geranyl Pyrophosphate Section 28.2 Figure 28.2... 

Some isopentenyl pyrophosphate is converted to the isomer dimethylallyl pyrophosphate, by an isomerase that produces a mixture, isopentenyl pyrophosphate dimethylallyl pyrophosphate. From this point on, the carbon chain-length of the intermediates progressively increase this is followed by reduction to squalene, which has 30 carbon atoms in a folded chain and no oxygen atoms (Chap. 6). The conversion of isopentenyl pyrophosphate to squalene is shown in Fig. 13-22. 

Cholesterol is primarily restricted to eukaryotic cells where it plays a number of roles. Undoubtedly, the most primitive function is as a structural component of membranes. Its metabolism to bile acids and the steroid hormones is relatively recent in the evolutionary sense. In this chapter, the pathway of cholesterol biosynthesis will be divided into segments which correspond to the chemical and biochemical divisions of this biosynthetic route. The initial part of the pathway is the 3-step conversion of acetyl-CoA to 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA). The next is the reduction of this molecule to mevalonate, considered to be the rate-controlling step in the biosynthesis of polyisoprenoids. From thence, a series of phosphorylation reactions both activate and decarboxylate mevalonate to isopen tenyl pyrophosphate, the true isoprenoid precursor. After a rearrangement to the allylic pyrophosphate, dimethylallyl pyrophosphate, a sequence of l -4 con-... 

Cholesterol, which is present in brain and in almost all tissues, is synthesised from isopentenyl pyrophosphate via squalene, farnesyl and geranyl pyrophosphates. The synthesis of squalene commences with the isomerisation of isopentenyl pyrophosphate to dimethylallyl pyrophosphate, after which successive condensations take place according to Equation 11.118. The hydrocarbon squalene is then transformed into the tetracyclic steroidal configuration of lanosterol by appropriate enzymes, and this is followed by conversion into cholesterol. Cholesterol is the precursor to most other steroids in the body. 

Biosynthetically, majority of terpenoids are formed via the mevalonic acid, but they may also be formed through methyl-erythritol-4-phosphate (MEP) pathway. The C5 isoprene unit which can be linked together head to tail to form linear chains or cyclized to form rings is considered the building blocks of terpenes. Rather the C5 units exist as isopentenyl pyrophosphate or its isomer dimethylallyl pyrophosphate by enzymatic conversion and phosphorylation from mevalonic acid. The IPP may be considered as the precursor of hemiterpenes. In the biosynthesis of mono- and higher terpenes/terpenoids, the starting molecule is DMAPP, which... 

MECHANISM FOR THE CONVERSION OF ISOPENTYL PYROPHOSPHATE TO DIMETHYLALLYL PYROPHOSPHATE... 

The location of the label from C(2) of mevalonate in the methyl group of chanoclavine I (Fehr et al, 1966) suggested a second cis-trans isomerization during the synthesis of chanoclavine I. In the conversion of isopentenyl pyrophosphate to dimethylallyl pyrophosphate, C(2) of mevalonate becomes the trans-mQihy group of dimethylallyl pyrophosphate (Popjak and Corn-forth, 1966). Because the label is located in the cw-methyl group of chanoclavine I, a cis-trans isomerization apparently occurs in the formation of chanoclavine I from dimethylallyl pyrophosphate. 

Carotenoids are synthesized from the basic C5 terpenoid precursor isopentenyl pyrophosphate (IPP) and dimethylallyl diphosphate (DMAPP). These precursors can be obtained from two distinct pathways the mevalonate pathway (MVA) and the non-MVA pathway also known as 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway [84, 85]. All eukaryotes use the MVA pathway, whereas plant plastids and most bacteria use the MEP pathway [86,87]. Some bacteria also use the MVA pathway [84]. In the MEP pathway, the first step in IPP biosynthesis is the formation of l-deoxy-D-xylulose-5-phosphate (DXP) from pyruvate and glyceraldehyde-3-phosphate catalyzed by DXP synthase (Figure 10.7). DXP is then reduced to MEP by DXP reductase. Additional MEP pathway enzymes are then used in subsequent reactions for converting MEP to IPP, which is isomer-ized to DMAPP by the enzyme IPP isomerase. The MVA pathway begins with the conversion of three molecules of acetyl-CoA to MVA through acetoacetyl-CoA... 

---