Biochemistry of PUFA Double Bond Isomerases Producing Conjugated Linoleic Acid

Abstract

The biotransformation of linoleic acid (LA) into conjugated linoleic acid (CLA) by microorganisms is a potentially useful industrial process. In most cases, however, the identities of proteins involved and the details of enzymatic activity regulation are far from clear. Here we summarize available data on the reaction mechanisms of CLA-producing enzymes characterized until now, from Butyrivibrio fibrisolvens, Lactobacillus acidophilus, Ptilota filicina, and Propionibacterium acnes. A general feature of enzymatic LA isomerization is the protein-assisted abstraction of an aliphatic hydrogen atom from position C-11, while the role of flavin as cofactor for the double bond activation in CLA-producing enzymes is also discussed with regard to the recently published three-dimensional structure of an isomerase from P. acnes. Combined data from structural studies, isotopic labeling experiments, and sequence comparison suggest that at least two different prototypical active site geometries occur among polyunsaturated fatty acid (PUFA) double bond isomerases.

Preparation of conjugated linoleic acid enriched derivatives by conventional and biphasic isomerisation

“…Linoleic acid was demonstrated to affect bacterial cell division (Jenkins et al 2008;Liavonchanka & Feussner 2008). Therefore, ruminal microflora had to develop a protective metabolic pathway, the biohydrogenation of double bonds in PUFAs.…”

“…), which carries out bioconversion of linoleic acid into (9Z,11E)-octadeca-9,11-dienoic acid (rumenic acid). Thus, the isomerase system has a physiological function (Kepler et al 1971;Hunter et al 1976;Devillard et al 2006;Liavonchanka & Feussner 2008). It is the first step of the linoleic acid biotransformation cascade resulting in the formation of stearic acid.…”

“…Enzymatic activity of linoleic acid ∆ 12 -cis,∆ 11 -trans isomerase is interesting when positional and geometric isomerisation of the pentadienyl system occurs without any activation by functional groups (Kepler et al 1971;Hunter et al 1976;Devillard et al 2006;Jenkins et al 2008;Liavonchanka & Feussner 2008 ). Analogical PUFA isomerases were described to be present in other bacteria (lactobacillus acidophilus, propionibacterium acnes, Bifidobacterium species) and red algae (ptilota filicina).…”

“…Active sites of isomerases consist of three domains forming the hydrophobic channel inside the enzyme, from which one has non-covalently bound flavin adenine dinucleotide (FAD). Enzymatic hydrogen abstraction from the C-11 bis-allylic position (pK a = 35) and subsequent double bond allylic shift occur only with free PUFAs (Liavonchanka et al 2006;Liavonchanka & Feussner 2008;Okuyama & Maskill 2014). First of all, triacylglycerol ester bonds have to be cleaved in order to release fatty acid substrates.…”

“…However, the concerted reaction mechanism and radical isomerisation in the absence of oxygen were not completely excluded. PUFA isomerase reverts to the initial state after the product [(9Z,11E)-octadeca-9,11-dienoic acid or (10E,12Z)-octadeca-10,12-dienoic acid] dissociates the active site (Kepler et al 1971;Liavonchanka et al 2006;Liavonchanka & Feussner 2008). …”