# Undecaprenyl phosphate
**Undecaprenyl phosphate** (Und-P, C\(_{55}\)-P), also known as bactoprenol or bactoprenyl phosphate, is an essential 55-carbon long-chain isoprenoid lipid that serves as the carrier lipid for bacterial cell-envelope glycan biosynthesis. It carries hydrophilic sugar intermediates across the hydrophobic cytoplasmic membrane so that cell-wall polymers can be assembled and polymerized outside the cytoplasm[1](https://journals.asm.org/doi/10.1128/ecosalplus.4.7.1.7). It is the common lipid carrier in bacteria, although decaprenyl phosphate is used by some mycobacteria and nonaprenyl phosphate by [Paracoccus denitrificans](https://www.edgepedia.org/paracoccus-denitrificans)[2](https://academicjournals.org/articles/1009902522) • [3](https://academic.oup.com/femsre/article/32/2/208/2683939).
| Key fact | Detail |
|---|---|
| Identity | C\(_{55}\) polyisoprenoid monophosphate, also called bactoprenol; the classical bacterial glycosyl carrier lipid[1](https://journals.asm.org/doi/10.1128/ecosalplus.4.7.1.7) • [3](https://academic.oup.com/femsre/article/32/2/208/2683939) |
| Polymers served | Peptidoglycan, lipopolysaccharide O antigen, wall teichoic acids, capsular polysaccharides, enterobacterial common antigen, membrane-derived oligosaccharides, and N-linked protein glycosylation in some prokaryotes[1](https://journals.asm.org/doi/10.1128/ecosalplus.4.7.1.7) • [3](https://academic.oup.com/femsre/article/32/2/208/2683939) |
| De novo synthesis | UppS, a soluble cis-prenyltransferase, condenses eight isopentenyl pyrophosphate (C\(_5\)-PP) units onto farnesyl pyrophosphate (C\(_{15}\)-PP) to form undecaprenyl pyrophosphate (C\(_{55}\)-PP), which is then dephosphorylated to the active monophosphate[1](https://journals.asm.org/doi/10.1128/ecosalplus.4.7.1.7) • [4](https://pubmed.ncbi.nlm.nih.gov/22471620/) |
| Dephosphorylation enzymes in E. coli | BacA (UppP) and three PAP2-family phosphatases, YbjG, LpxT, and PgpB; none is essential alone, but simultaneous inactivation of bacA, ybjG, and pgpB is lethal[1](https://journals.asm.org/doi/10.1128/ecosalplus.4.7.1.7) |
| Pool composition in E. coli | 22% Und-P (75 nmol/g) and 78% Und-PP (260 nmol/g), with no detectable free undecaprenol reserve[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC3253937/) |
| Antibiotic relevance | Bacitracin blocks recycling by sequestering C\(_{55}\)-PP; amphomycin and friulimicin bind undecaprenyl phosphate directly[6](https://pmc.ncbi.nlm.nih.gov/articles/PMC8169544/) |
| Eukaryotic counterpart | Dolichyl phosphate, which differs by a saturated α-isoprene unit and serves analogous carrier functions in eukaryotes and archaea[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC4050452/) |
## Function as a carrier lipid
Nearly all bacterial glycoconjugates, including peptidoglycan, capsules, exopolysaccharides, LPS O-antigens, teichoic acids, and lipoglycans, have their glycan moiety assembled on and transported by Und-P[8](https://pmc.ncbi.nlm.nih.gov/articles/PMC12826051/). The sugar unit is transferred from a nucleotide-sugar intermediate to the lipid carrier by a glycosyltransferase at the cytoplasmic face of the inner membrane; the lipid-linked intermediate is then flipped to the outer leaflet, where polymerization occurs[1](https://journals.asm.org/doi/10.1128/ecosalplus.4.7.1.7). In peptidoglycan synthesis, the membrane steps begin with transfer of the phospho-MurNAc-pentapeptide moiety from the nucleotide precursor to Und-P, forming Lipid I, to which a GlcNAc unit is added to yield Lipid II[9](https://academic.oup.com/femsre/article/32/2/386/2684068). Specialized flippases such as MurJ and TagGH then translocate these glycolipids across the membrane[10](https://www.nature.com/articles/s41467-018-03547-8).
Because a single lipid participates in the synthesis of many wall polymers, its pool has been considered a potential control point that prevents imbalance in the formation of the cell envelope as a whole[3](https://academic.oup.com/femsre/article/32/2/208/2683939). Cells that cannot recycle Und-P produce too few cell-wall precursors to sustain growth and eventually lyse[8](https://pmc.ncbi.nlm.nih.gov/articles/PMC12826051/).
## Structure and relation to dolichyl phosphate
Und-P is a linear polymer of eleven isoprene units with a mixed E,Z stereochemistry; the isoprene units are added in the cis configuration onto a short all-trans oligoprene precursor[3](https://academic.oup.com/femsre/article/32/2/208/2683939) • [7](https://pmc.ncbi.nlm.nih.gov/articles/PMC4050452/). Its terminal isoprene unit proximal to the phosphate group is unsaturated, whereas in eukaryotes and archaea this α-position is saturated, a difference that requires an additional reduction step and produces dolichyl phosphate[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC4050452/). In all organisms these polyprenyl phosphates fulfill a similar function: facilitating translocation of a polar head group, such as mono- or oligosaccharides, across a highly hydrophobic membrane environment[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC4050452/).
Although C\(_{55}\)-P is the classical bacterial form, shorter homologs perform the same role in some species: decaprenyl phosphate (C\(_{50}\)-P) in mycobacterial species and nonaprenyl phosphate (C\(_{45}\)-P) in *Paracoccus denitrificans*[3](https://academic.oup.com/femsre/article/32/2/208/2683939). Und-P also carries monosaccharide modifications in some pathways, such as undecaprenyl-phosphate-L-4-amino-4-deoxy-arabinose in lipid A modification of [Gram-negative bacteria](https://www.edgepedia.org/gram-negative-bacteria)[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC4050452/).
## Biosynthesis
De novo synthesis proceeds in two steps. First, the essential undecaprenyl pyrophosphate synthase (UppS), a soluble cis-prenyltransferase, catalyzes eight consecutive condensations of isopentenyl pyrophosphate onto farnesyl pyrophosphate, generating C\(_{55}\)-PP in the cytoplasm[1](https://journals.asm.org/doi/10.1128/ecosalplus.4.7.1.7) • [4](https://pubmed.ncbi.nlm.nih.gov/22471620/). Second, C\(_{55}\)-PP is dephosphorylated to the monophosphate form before the carrier can accept a sugar unit at the cytoplasmic face of the membrane[1](https://journals.asm.org/doi/10.1128/ecosalplus.4.7.1.7).
In *Escherichia coli*, four integral membrane proteins catalyze this dephosphorylation: BacA (also called UppP) and three members of the PAP2 (type-2 phosphatidic acid phosphatase) superfamily, YbjG, LpxT, and PgpB[1](https://journals.asm.org/doi/10.1128/ecosalplus.4.7.1.7). The active sites of LpxT, PgpB, and YbjG face the periplasm, suggesting that PAP2 enzymes are mainly involved in recycling C\(_{55}\)-PP released at the outer surface, while UppP has been proposed to act during de novo synthesis and possibly as a lipid flippase[1](https://journals.asm.org/doi/10.1128/ecosalplus.4.7.1.7) • [11](https://www.sciencedirect.com/science/article/abs/pii/S0022283620302588). LpxT additionally transfers the phosphate released from C\(_{55}\)-PP onto the lipid A moiety of lipopolysaccharide, producing a lipid-A 1-diphosphate form that accounts for one-third of total lipid A in wild-type E. coli[1](https://journals.asm.org/doi/10.1128/ecosalplus.4.7.1.7).
## Recycling and the undecaprenol alternative
After each polymerization round, the lipid is released as C\(_{55}\)-PP on the outer surface of the inner membrane and must be converted back to the monophosphate and returned to the cytoplasmic side[1](https://journals.asm.org/doi/10.1128/ecosalplus.4.7.1.7). This recycling is essential: cells unable to recycle Und-P cannot sustain cell-wall precursor production and lyse[8](https://pmc.ncbi.nlm.nih.gov/articles/PMC12826051/).
A second route to Und-P exists in [Gram-positive bacteria](https://www.edgepedia.org/gram-positive-bacteria). Several Gram-positive species, including *Staphylococcus aureus* and *Bacillus subtilis*, contain significant amounts of free undecaprenol (Und-OH), which is phosphorylated to Und-P by an enzyme homologous to the E. coli diacylglycerol kinase DgkA[12](https://pmc.ncbi.nlm.nih.gov/articles/PMC9098691/) • [13](https://pubmed.ncbi.nlm.nih.gov/29198165/). Undecaprenol has not been found in Gram-negative bacteria, and no undecaprenol kinases have been identified in that group; E. coli contains only Und-P and Und-PP with no reserve pool of free undecaprenol[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC3253937/). The origin and function of the Gram-positive undecaprenol pool are not clearly established[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC4050452/).
## Pool sizes in Gram-negative and Gram-positive bacteria
Measured pools differ markedly between the two groups. In E. coli, Und-P represents 22% of the undecaprenyl derivatives (75 nmol/g) and Und-PP 78% (260 nmol/g)[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC3253937/). Estimates of Lipid I/II, the peptidoglycan precursors carried on the lipid, are much higher in Gram-positive species: metabolic labeling indicated about 34,000 Lipid I/II molecules per cell of *Bacillus megaterium*, and antibiotic binding-site counts suggested 50,000 peptidoglycan precursors in *S. aureus*, 70,000 in *Micrococcus luteus*, and 200,000 in *Staphylococcus simulans*[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC3253937/). In S. aureus this amount would represent over 40% of the total undecaprenyl-derivative pool[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC3253937/).
These differences parallel wall architecture: Gram-positive peptidoglycan layers are 20 to 80 nm thick, compared with 7 to 8 nm in Gram-negative bacteria, so larger precursor pools are expected[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC3253937/).
## Antibiotics targeting the carrier lipid cycle
Several antibiotics act on the carrier lipid or its cycle. Bacitracin inhibits the metabolism of undecaprenyl pyrophosphate to undecaprenyl phosphate, preventing recycling of the carrier[6](https://pmc.ncbi.nlm.nih.gov/articles/PMC8169544/); it sequesters C\(_{55}\)-PP, provoking loss of cell integrity and lysis[14](https://www.sciencedirect.com/topics/immunology-and-microbiology/bacitracin). Amphomycin and friulimicin bind undecaprenyl phosphate directly[6](https://pmc.ncbi.nlm.nih.gov/articles/PMC8169544/). [Colicin M](https://www.edgepedia.org/colicin-m) exerts its bacteriolytic effect by enzymatic degradation of undecaprenyl phosphate-linked peptidoglycan precursors[1](https://journals.asm.org/doi/10.1128/ecosalplus.4.7.1.7). Because virtually every step in the Und-P synthesis pathway is essential, the carrier lipid cycle is regarded as a promising target for new antibiotic development[8](https://pmc.ncbi.nlm.nih.gov/articles/PMC12826051/) • [15](https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/2211-5463.70066).
## References
1. [Touzé T, Mengin-Lecreulx D (2008). Undecaprenyl Phosphate Synthesis. EcoSal Plus.](https://journals.asm.org/doi/10.1128/ecosalplus.4.7.1.7)
2. [Coker OO, Palittapongarnpim P (2012). Current understanding of de novo synthesis of bacterial lipid carrier (undecaprenyl phosphate): More enzymes to be discovered. African Journal of Microbiology Research.](https://academicjournals.org/articles/1009902522)
3. [Bouhss A, Trunkfield AE, Bugg TDH, Mengin-Lecreulx D (2008). The biosynthesis of peptidoglycan lipid-linked intermediates. FEMS Microbiology Reviews.](https://academic.oup.com/femsre/article/32/2/208/2683939)
4. [Liang PH (2009). Undecaprenyl diphosphate synthase, a cis-prenyltransferase synthesizing lipid carrier for bacterial cell wall biosynthesis. Biochemical Journal / PubMed.](https://pubmed.ncbi.nlm.nih.gov/22471620/)
5. [Bajaj R, McNeil MB, Seipke RF, et al. (2011). At the membrane frontier: A prospectus on the remarkable evolutionary conservation of polyprenols and polyprenyl-phosphates. PMC.](https://pmc.ncbi.nlm.nih.gov/articles/PMC3253937/)
6. [Natural products that target the cell envelope. PMC.](https://pmc.ncbi.nlm.nih.gov/articles/PMC8169544/)
7. [Manat G, Roure S, Auger R, et al. (2014). Deciphering the Metabolism of Undecaprenyl-Phosphate: The Bacterial Cell-Wall Unit Carrier at the Membrane Frontier. PMC.](https://pmc.ncbi.nlm.nih.gov/articles/PMC4050452/)
8. [Jorgenson MA et al. (2025). Pardon the interruption: how Und-P sequestration has reshaped our understanding of the bacterial cell envelope. Journal of Bacteriology.](https://pmc.ncbi.nlm.nih.gov/articles/PMC12826051/)
9. [Evolution of peptidoglycan biosynthesis under the selective pressure of antibiotics in Gram-positive bacteria. FEMS Microbiology Reviews.](https://academic.oup.com/femsre/article/32/2/386/2684068)
10. [Workman SD, Strynadka NCJ (2018). Crystal structure of an intramembranal phosphatase central to bacterial cell-wall peptidoglycan biosynthesis and lipid recycling. Nature Communications.](https://www.nature.com/articles/s41467-018-03547-8)
11. [Mohn WW et al. (2020). A Slippery Scaffold: Synthesis and Recycling of the Bacterial Cell Wall Carrier Lipid. Journal of Molecular Biology.](https://www.sciencedirect.com/science/article/abs/pii/S0022283620302588)
12. [The Bacterial Cell Wall: From Lipid II Flipping to Polymerization. PMC.](https://pmc.ncbi.nlm.nih.gov/articles/PMC9098691/)
13. [Kawakami N, Fujisaki S (2018). Undecaprenyl phosphate metabolism in Gram-negative and Gram-positive bacteria. Bioscience, Biotechnology, and Biochemistry.](https://pubmed.ncbi.nlm.nih.gov/29198165/)
14. [Bacitracin - an overview. ScienceDirect Topics.](https://www.sciencedirect.com/topics/immunology-and-microbiology/bacitracin)
15. [Analysis of the regulation of undecaprenyl diphosphate dephosphorylation in Escherichia coli. FEBS Letters / Wiley.](https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/2211-5463.70066)
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*Topic: Encyclopedia › Life and health › Biological foundations › Biochemistry and metabolism › Enzyme classes and activities › Glycosyltransferases and glyco-enzyme activities › Dolichol-linked and polysaccharide-synthesizing enzymes › Lipid-linked sugar carrier biology (general)*
*Initially written Sep 17, 2026 · Reviewed: Sep 30, 2026; Oct 21, 2026 · Edited: Sep 30, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*
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License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license