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Cytochrome c -type cis / trans fatty acid isomerase (CTI) has been proposed to control cis / trans isomerism of unsaturated fats in lipid-related food products. A gene encoding wildtype CTI from Pseudomonas putida KT2440 was introduced into the pET26b/pEC86 co-expression system, and the heme C cofactor was covalently bound into the expressed CTI protein through in vivo cytochrome c maturation. The recombinant CTI, purified from Escherichia coli BL21(DE3), catalyzed the cis / trans isomerization of three edible monounsaturated fatty acids. It exhibited strong substrate selectivity for palmitoleic acid (C 16:1 , cis -Δ9), reaching an 80.93 ± 1.78% conversion at reaction equilibrium. Notably, its promiscuity for other fatty acids (oleic acid: 29.21 ± 5.01% and cis -vaccenic acid: 51.21 ± 0.05%) was observed. Under the optimum reaction conditions (pH 7.5 and 15 °C), the kinetic parameters (V max , K m , and k cat) of CTI were derived as 0.035 mM min−1, 0.267 mM, and 0.141 sec−1, respectively, and the final catalytic efficiency (k cat /K m) was calculated as 5.26 × 102 M−1 s−1. Furthermore, structural properties of CTI were analyzed using deep learning-based protein structure prediction, suggesting the potential for specificity variability by altering loop dynamics and helix interactions surrounding the heme-binding motif. The following results would provide theoretical and practical information for CTI enzymes as novel promising industrial catalysts to control cis / trans isomerism of lipids in food products. [Display omitted] • Cis / trans fatty acid isomerase (CTI) is a bacterial cytochrome c -type hemoprotein. • The recombinant CTI was expressed in the pET26b/pEC86 co-expression system. • The recombinant CTI showed substrate promiscuity towards unsaturated fatty acids. • The recombinant CTI showed strong substrate selectivity against palmitoleic acid. • Deep learning-based structural prediction demonstrated the mode of action of CTI. [ABSTRACT FROM AUTHOR]

Abstract: The preparation of six phenylphosphonates (and phosphonic acid derivatives) bearing a sulfur group in ortho position was accomplished via either a [1,3]- or a [1,4]-sigmatropic rearrangement. Their complexation with different platinum sources has been studied and the new platinum complexes obtained were characterized by NMR spectroscopy (1H, 13C, 31P and 195Pt). Three runs of experiments were performed. The first was the reaction of ligands 1 and 2 bearing one sulfide and a phosphonate diester functions with potassium tetrachloroplatinate. In the obtained complexes, two molecules of ligand chelate the metal only by the sulfur atom. We were able to observe by 195Pt and 31P NMR spectroscopy the trans to cis rearrangement of a dichloro-methyl-(o-phosphorylbenzyl)sulfide platinum(II) complex upon time, leading to two new species, which are diastereomers of the cis-complex. The second set of experiments involved ligands 1, 2 and 3 bearing one sulfide or sulfoxide and a phosphonate diester moieties, cisplatin and one equivalent of silver nitrate. In the resulting complexes the platinum is coordinated by the sulfur atom of one molecule of ligand. In the third run, the reaction between ligands 4, 5, and 6 bearing one sulfide or sulfoxide and one phosphonic acid or one phosphonic monoester group and the cisplatin diaqua form led to O,S–Pt chelates. [Copyright &y& Elsevier]

Abstract: The influence of α-cis- and α-trans-polyprenols on the structure and properties of model membranes was analyzed. The interaction of Ficaprenol-12 (α-cis-Prenol-12, α-Z-Prenol-12) and Alloprenol-12 (α-trans-Prenol-12, α-E-Prenol-12) with model membranes was compared using high performance liquid chromatography (HPLC), differential scanning calorimetry (DSC) and fluorescent methods. l-α-Phosphatidylcholine from egg yolk (EYPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) as the main lipid components of unilamellar (SUVs) and multilamellar (MLVs) vesicles were used. The two-step extraction procedure (n-pentane and hexane, respectively) allowed to separately analyze the fractions of polyprenol as non-incorporated (PrenolNonInc) and incorporated (PrenolInc) into liposomes. Consequently, distribution coefficients, P′, describing the equilibrium of prenol content between phospholipid (EYPC) membrane and the aqueous phase gave different log P′ for α-cis- and α-trans-Prenol-12, indicating that the configuration of the α-terminal residue significantly alters the hydrophobicity of the polyisoprenoid molecule and consequently the affinity of polyprenols for EYPC membrane. In fluorescence experiments α-trans-Pren-12 increased up to 1.7-fold the permeability of EYPC bilayer for glucose while the effect of α-cis-Pren-12 was almost negligible. Considerable changes of thermotropic behavior of DPPC membranes in the presence of both prenol isomers were observed. α-trans-Pren-12 completely abolished the pretransition while in the case of α-cis-Pren-12 it was noticeably reduced. Furthermore, for both prenol isomers, the temperature of the main phase transition (T m ) was shifted by about 1°C to lower values and the height of the peak was significantly reduced. The DSC analysis profiles also showed a new peak at 38.7°C, which may suggest the concomitant presence of more that one phase within the membrane. Results of these experiments and the concomitant occurrence of alloprenols and ficaprenols in plant tissues suggest that cis/trans isomerization of the α-residue of polyisoprenoid molecule might comprise a putative mechanism responsible for modulation of the permeability of cellular membranes. [Copyright &y& Elsevier]

Abstract: In a previous paper, we demonstrated that tissue trans fatty acids can not only derive from the diet but also be endogenously formed. The central focus of this study was to prove that the in vivo isomerization occurs via a radical process. Two different models of radical insult were used: CCl4 and AAPH injection to rats fed a diet completely free of trans isomers. Following this acute radical stress, a significant increase in unnatural trans fatty acid content of erythrocyte, kidney, and heart, but not liver, was observed. These results can be mainly explained by the high content, particularly in the liver, of antioxidant vitamins A and E that exhibit also an “anti-isomerizing” effect. Since during ageing cellular components are exposed to increasing radical insults, the observation of a significant trans fatty acid accumulation in 30-month-old rats could confirm that the in vivo formation of unnatural isomers is due to a radical process. Trans fatty acids can influence the physical characteristics of bilayer microdomains, affecting membrane properties and functions; thus, knowledge of biological radical species responsible for cis/trans isomerization and their possible sources can provide protective systems for preserving lipid geometry. [Copyright &y& Elsevier]

Abstract: The kinetics of Z-(cis)/E-(trans) isomerization of enalapril was investigated by reversed phase high-performance liquid chromatography (RP-HPLC) using a monolith ODS column under a series of different temperature and pH conditions. At a neutral pH 7, the rate (k obs) of Z-(cis)/E-(trans) isomerization of enalapril at 4°C (9.4×10−3 min−1) is much lower than at 23°C (1.8×10−1 min−1), while the fractional concentration of Z-(cis) isomer is always higher than that of E-(trans) isomer in the pH range 2–7. The fractional concentration of the E-(trans) isomer becomes a maximum (about 40%) in the pH range 3–6, where enalapril exists as a zwitterion. The hydrophobicity (log P O/W) of both isomers was estimated by high-speed counter-current chromatography (HSCCC). Normal phase HSCCC separation using a tert-butyl methyl ether–acetonitrile–20mM potassium phosphate buffer (pH 5) two-phase solvent system (2:2:3, v/v/v) at 4°C was effective in partially separating the isomers, and the partition coefficient (K) of each isomer was directly calculated from the retention volume (V R). The log P O/W values of Z-(cis) and E-(trans) isomers were −0.46 and −0.65, respectively. [Copyright &y& Elsevier]

Abstract: Trans isomers of unsaturated fatty acids are absorbed from the diet, due to their presence in diary fat and hydrogenated vegetable oils, and health concern has risen due to their effects on lipid risk factors in cardiovascular diseases. On the basis of the efficiency of the thiyl-radical-catalyzed cis/trans isomerization in vitro and the presence of many sulfur-containing compounds in the cell, the aim of this study was to demonstrate that trans geometry of lipid double bonds can be endogenously generated within membrane phospholipids. The study reports trans fatty acids occurrence in tissue and erythrocyte phospholipids of young adult rats fed a diet completely free of trans isomers. Results show that tissues are differently prone to the endogenous isomerization and that, following a free radical attack, trans fatty acids can reach very high amounts. The effectiveness of this process is considerably inhibited in the presence of all-trans retinol, confirming previous data in model membranes. Our results suggest that geometrical isomerization of unsaturated fatty acids, which causes a structural modification of membrane lipids and may influence basic membrane properties and vital biochemical functions, can occur under radical stress conditions and could be efficiently prevented by vitamin A. [Copyright &y& Elsevier]

Peptidyl–prolyl cis/trans isomerization, observed in the native state of an increasing number of proteins, is of considerable biological significance. The first evidence for an asymmetric transmission along the polypeptide chain of the structural effects of prolyl isomerization is now derived from the statistics of the Cα/Cα-atom distance distributions in the crystal structures of 848 non-homologous proteins. More detailed information on how isomerization affects segments adjacent to proline is obtained from crystal structures of proteins, that are more than 95% homologous, and that exhibit two different states of isomerization at a particular prolyl bond. The resulting 64 cases, which represent 3.8% of the database used, form pairs of coordinates which were analyzed for the existence of isomer-specific intramolecular nonbonded Cα/Cα-atom distances around the critical proline, and for the positional preferences for particular amino acids in the isomeric sequence segment. The probability that a native protein exhibits both prolyl isomers in the crystalline state increases in particular with a Pro at the third position N-terminal to the isomeric bond (−3 position), and with Ser, Gly and Asp at the position preceding the isomeric bond (−1 position). Structural alignment of matched pairs of isomeric proteins generates three classes with respect to position-specific distribution of Cα-atom displacements around an isomeric proline imide bond. In the majority of cases the distribution of these intermolecular isomer-specific Cα-atom distances shows a symmetric behavior for the N-terminal and C-terminal segment flanking the proline residue, and the magnitude did not exceed 1.3±0.6 A˚ including the Cα atoms in proximity to the prolyl bond. However, in the remaining 12 protein pairs the structural changes are unidirectional relative to the isomerizing bond whereby the magnitude of the isomer-specific effect exceeds 3.0±2.0 A˚ even at positions remote to proline. Interestingly, the magnitude of the intramolecular isomer-specific Cα atom displacements reveals a lever–arm amplification of the isomerization-mediated structural changes in a protein backbone. The observed backbone effects provide a structural basis for isomer-specific reactions of proline-containing polypeptides, and thus may play a role in biological recognition and regulation. [Copyright &y& Elsevier]