Lipase-catalyzed acylation of naringin with palmitic acid in highly concentrated homogeneous solutions

Efficient biosynthesis of prunin in methanol cosolvent system by an organic solvent-tolerant α-L-rhamnosidase from Spirochaeta thermophila

Prunin of desirable bioactivity and bioavailability can be transformed from plant-derived naringin by the key enzyme α-L-rhamnosidase. However, the production was limited by unsatisfactory properties of α-L-rhamnosidase such as thermostability and organic solvent tolerance. In this study, biochemical characteristics, and hydrolysis capacity of a novel α-L-rhamnosidase from Spirochaeta thermophila (St-Rha) were investigated, which was the first characterized α-L-rhamnosidase for Spirochaeta genus. St-Rha showed a higher substrate specificity towards naringin and exhibited excellent thermostability and methanol tolerance. The Km of St-Rha in the methanol cosolvent system was decreased 7.2-fold comparing that in the aqueous phase system, while kcat/Km value of St-Rha was enhanced 9.3-fold. Meanwhile, a preliminary conformational study was implemented through comparative molecular dynamics simulation analysis to explore the mechanism underlying the methanol tolerance of St-Rha for the first time. Furthermore, the catalytic ability of St-Rha for prunin preparation in the 20% methanol cosolvent system was explored, and 200 g/L naringin was transformed into 125.5 g/L prunin for 24 h reaction with a corresponding space-time yield of 5.2 g/L/h. These results indicated that St-Rha was a novel α-L-rhamnosidase suitable for hydrolyzing naringin in the methanol cosolvent system and provided a better alternative for improving the efficient production yield of prunin.

Effects of magnetic fields on the enzymatic synthesis of naringin palmitate

The effects of magnetic fields on the enzymatic synthesis of naringin palmitate were studied. Both immobilized Candida Antarctica lipase B (I-CALB) and I-CALB tert-amyl alcohol solution were treated with magnetic fields of 100, 300, or 500 mT for 1, 2, or 3 h. Characteristics including the initial rate and the conversion yields after 24 h of reaction with magnetized I-CALB (M-I-CALB) and magnetized I-CALB tert-amyl alcohol solution (M-I-CALB-S) were investigated. Magnetic field application to both I-CALB and I-CALB-S influenced I-CALB activity. Enzyme activity increased for M-I-CALB and M-I-CALB-S with some intensities and durations and reached maxima at certain frequencies. Enzyme inactivation was only found with M-I-CALB exposed to a strong magnetic field (500 mT) for a long time (3 h). Unlike M-I-CALB, M-I-CALB-S exposed to a strong magnetic field for a long time (500 mT, 3 h) showed greater activity enhancement relative to I-CALB. Fourier transform infrared spectroscopy (FT-IR) results showed that the relative secondary structure content of free CALB was changed only slightly by the differing magnetic field intensities and durations. These findings should prove valuable for using magnetic fields in enzymatic reactions.

Immobilized CALB (I-CALB) and I-CALB solution was treated by magnetic fields and enzymatic reactions with them were compared.

Naringin lauroyl ester inhibits lipopolysaccharide-induced activation of nuclear factor κB signaling in macrophages

Naringin (Nar) has antioxidant and anti-inflammatory properties. It was recently reported that enzymatic modification of Nar enhanced its functions. Here, we acylated Nar with fatty acids of different sizes (C2–C18) using immobilized lipase from Rhizomucor miehei and investigated the anti-inflammatory effects of these molecules. Treatment of murine macrophage RAW264.7 cells with Nar alkyl esters inhibited lipopolysaccharide (LPS)-induced nitric oxide (NO) production, with Nar lauroyl ester (Nar-C12) showing the strongest effect. Furthermore, Nar-C12 suppressed the LPS-induced expression of inducible NO synthase by blocking the phosphorylation of inhibitor of nuclear factor (NF)-κB-α as well as the nuclear translocation of NF-κB subunit p65 in macrophage cells. Analysis of Nar-C12 uptake in macrophage cells revealed that Nar-C12 ester bond was partially degraded in the cell membrane and free Nar was translocated to the cytosol. These results indicate that Nar released from Nar-C12 exerts anti-inflammatory effects by suppressing NF-κB signaling pathway.

Investigation of the interaction of naringin palmitate with bovine serum albumin: spectroscopic analysis and molecular docking

BACKGROUND

Bovine serum albumin (BSA) contains high affinity binding sites for several endogenous and exogenous compounds and has been used to replace human serum albumin (HSA), as these two compounds share a similar structure. Naringin palmitate is a modified product of naringin that is produced by an acylation reaction with palmitic acid, which is considered to be an effective substance for enhancing naringin lipophilicity. In this study, the interaction of naringin palmitate with BSA was characterised by spectroscopic and molecular docking techniques.

METHODOLOGY/PRINCIPAL FINDINGS

The goal of this study was to investigate the interactions between naringin palmitate and BSA under physiological conditions, and differences in naringin and naringin palmitate affinities for BSA were further compared and analysed. The formation of naringin palmitate-BSA was revealed by fluorescence quenching, and the Stern-Volmer quenching constant (KSV ) was found to decrease with increasing temperature, suggesting that a static quenching mechanism was involved. The changes in enthalpy (ΔH) and entropy (ΔS) for the interaction were detected at -4.11 ± 0.18 kJ·mol(-1) and -76.59 ± 0.32 J·mol(-1)·K(-1), respectively, which indicated that the naringin palmitate-BSA interaction occurred mainly through van der Waals forces and hydrogen bond formation. The negative free energy change (ΔG) values of naringin palmitate at different temperatures suggested a spontaneous interaction. Circular dichroism studies revealed that the α-helical content of BSA decreased after interacting with naringin palmitate. Displacement studies suggested that naringin palmitate was partially bound to site I (subdomain IIA) of the BSA, which was also substantiated by the molecular docking studies.

CONCLUSIONS/SIGNIFICANCE

In conclusion, naringin palmitate was transported by BSA and was easily removed afterwards. As a consequence, an extension of naringin applications for use in food, cosmetic and medicinal preparations may be clinically and practically significant, especially in the design of new naringin palmitate-inspired drugs.

Enzymatic Synthesis of Naringin Palmitate

Naringin esters are paid more attention in medical and functional food industry than naringin due to their higher stability and solubility in lipidic environments. Naringin palmitic acid esters were enzymatically synthesized with naringin and palmitic acid. The effects of solvent type, temperature, concentration and types of enzymes and the molar ratio of substrates on the conversion of naringin were investigated. Novozym 435 performed higher catalytic ability in tert-amyl alcohol in the esterification of naringin with palmitic acid. The conversion yield of naringin increased with the increase of temperature (30-70°C) and of the concentration of enzyme. The structure of the naringin palmitate was characterized by FT-IR, 1H-NMR and HPLC-MS. 1H-NMR spectroscopic analysis indicated the presence of an ester bond on the C-6 of the glucose moiety of naringin molecule.

Molten globule-triggered inactivation of a thermostable and solvent stable lipase in hydrophilic solvents

The use of lipase in hydrophilic solvent is usually hampered by inactivation. The solvent stability of a recombinant solvent stable lipase isolated from thermostable Bacillus sp. strain 42 (Lip 42), in DMSO and methanol were studied at different solvent-water compositions. The enzymatic activities were retained in up to 45% v/v solvent compositions. The near-UV CD spectra indicated that tertiary structures were perturbed at 60% v/v and above. Far-UV CD in methanol indicated the secondary structure in Lip 42 was retained throughout all solvent compositions. Fluorescence studies indicated formations of molten globules in solvent compositions of 60% v/v and above. The enzyme was able to retain its secondary structures in the presence of methanol; however, there was a general reduction in beta-sheet and an increase in alpha-helix contents. The H-bonding arrangements triggered in methanol and DMSO, respectively, caused different forms of tertiary structure perturbations on Lip 42, despite both showing partial denaturation with molten globule formations.