The biosynthesis of steroids terpenes and acetogenins

Events that occur during or following biosynthesis include proteolysis , post-translational modification and protein folding . Proteolysis may remove N-terminal, C-terminal or internal amino-acid residues or peptides from the polypeptide. The termini and side-chains of the polypeptide may be subjected to post-translational modification . These modifications may be required for correct cellular localisation or the natural function of the protein. During and after synthesis, polypeptide chains often fold to assume, so called, native secondary and tertiary structures . This is known as protein folding and is typically required for the natural function of the protein.

In bacteria, the enzyme glutamate 5-kinase initiates the biosynthesis of proline by transferring a phosphate group from ATP onto glutamate. The next reaction is catalyzed by the enzyme pyrroline-5-carboxylate synthase (P5CS), which catalyzes the reduction of the ϒ-carboxyl group of L-glutamate 5-phosphate. This results in the formation of glutamate semialdehyde, which spontaneously cyclizes to pyrroline-5-carboxylate. Pyrroline-5-carboxylate is further reduced by the enzyme pyrroline-5-carboxylate reductase (P5CR) to yield a proline amino acid. [28]

The MEP pathway starts with the condensation of pyruvate and D-glyceraldehyde-3-phosphate to 1-deoxy-D-xylulose-5-phosphate (DXP or DOXP). The key isomers DMAPP and IPP are subsequently formed via a series of enzymatic steps starting with the conversion of DXP to 2C-methyl-D-erythritol-4-phosphate (MEP). Enzymes of this MEP pathway are attractive targets for the development of drugs targeting infectious diseases such as malaria and tuberculosis, because this pathway occurs in pathogenic prokaryotes but is absent in human metabolic pathways.

The conversion of HMG-CoA to mevalonate by HMG-CoA reductase is the rate-limiting step of cholesterol biosynthesis and is under strict regulatory control (see Figure 1 ). HMGR is the target of compounds that are effective in lowering serum cholesterol levels. Human HMG-CoA reductase consists of a single polypeptide chain of 888 amino acids. The amino-terminal residues are membrane bound and reside in the endoplasmic reticulum membrane, while the catalytic site of the protein resides in its cytoplasmic, soluble carboxy-terminal portion. A linker region connects the two portions of the protein.

Pilocarpine is found exclusively in species of Pilocarpus and the presence of other imidazole alkaloids has been reported in several species of the genus. Pilocarpine has several important pharmaceutical applications. Although several imidazole alkaloids related to pilocarpine have been reported in the previous years, little is still known about its biosynthetic route. At most, histidine has been reported as the precursor of pilocarpine. Based on our own previous reports and in an experiment where pilocarpine and related alkaloids (pilosine, trachyllophiline and anhydropilosine) were supplied to P. microphyllus leaves and the alkaloid profile analyzed by UPLC-MS, we suggest a biosynthesis pathway for pilocarpine. Further experiments using labeled precursors associated with transcriptome data may allow us to understand the whole biosynthesis pathway and its genetic control.

The biosynthesis of steroids terpenes and acetogenins

the biosynthesis of steroids terpenes and acetogenins

The conversion of HMG-CoA to mevalonate by HMG-CoA reductase is the rate-limiting step of cholesterol biosynthesis and is under strict regulatory control (see Figure 1 ). HMGR is the target of compounds that are effective in lowering serum cholesterol levels. Human HMG-CoA reductase consists of a single polypeptide chain of 888 amino acids. The amino-terminal residues are membrane bound and reside in the endoplasmic reticulum membrane, while the catalytic site of the protein resides in its cytoplasmic, soluble carboxy-terminal portion. A linker region connects the two portions of the protein.

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