IUBMB Enzyme Nomenclature


Accepted name: phthioceranic/hydroxyphthioceranic acid synthase

Reaction: (1) 8 (S)-methylmalonyl-CoA + palmitoyl-[(hydroxy)phthioceranic acid synthase] + 16 NADPH + 16 H+ = 8 CoA + C40-phthioceranyl-[(hydroxy)phthioceranic acid synthase] + 16 NADP+ + 8 CO2 + 8 H2O
(2) 7 (S)-methylmalonyl-CoA + palmitoyl-[(hydroxy)phthioceranic acid synthase] + 14 NADPH + 14 H+ = 7 CO2 + C37-phthioceranyl-[(hydroxy)phthioceranic acid synthase] + 14 NADP+ + 7 CoA + 7 H2O

Other name(s): msl2 (gene name); PKS2

Systematic name: (S)-methylmalonyl-CoA:palmitoyl-[(hydroxy)phthioceranic acid synthase] methylmalonyltransferase (phthioceranyl-[(hydroxy)phthioceranic acid synthase]-forming)

Comments: This mycobacterial polyketide enzyme produces the hepta- and octa-methylated fatty acids known as phthioceranic acids, and presumably their hydroxylated versions. Formation of hepta- and octamethylated products depends on whether the enzyme incorporates seven or eight methylmalonyl-CoA extender units, respectively. Formation of hydroxylated products may result from the enzyme skipping the dehydratase (DH) and enoylreductase (ER) domains during the first cycle of condensation [2].

Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number:


1. Sirakova, T.D., Thirumala, A.K., Dubey, V.S., Sprecher, H. and Kolattukudy, P.E. The Mycobacterium tuberculosis pks2 gene encodes the synthase for the hepta- and octamethyl-branched fatty acids required for sulfolipid synthesis. J. Biol. Chem 276 (2001) 16833-16839. [PMID: 11278910]

2. Gokhale, R.S., Saxena, P., Chopra, T. and Mohanty, D. Versatile polyketide enzymatic machinery for the biosynthesis of complex mycobacterial lipids. Nat. Prod. Rep. 24 (2007) 267-277. [PMID: 17389997]

3. Passemar, C., Arbues, A., Malaga, W., Mercier, I., Moreau, F., Lepourry, L., Neyrolles, O., Guilhot, C. and Astarie-Dequeker, C. Multiple deletions in the polyketide synthase gene repertoire of Mycobacterium tuberculosis reveal functional overlap of cell envelope lipids in host-pathogen interactions. Cell Microbiol 16 (2014) 195-213. [PMID: 24028583]

[EC created 2019]

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