Exploring the Diversity and Regulation of Apocarotenoid Metabolic Pathways in Plants

In plants, carotenoids are subjected to enzyme-catalyzed oxidative cleavage reactions as well as to non-enzymatic degradation processes, which produce various carbonyl products called apocarotenoids. These conversions control carotenoid content in different tissues and give rise to apocarotenoid hormones and signaling molecules, which play important roles in plant growth and development, response to environmental stimuli, and in interactions with surrounding organisms. In addition, carotenoid cleavage gives rise to apocarotenoid pigments and volatiles that contribute to the color and flavor of many flowers and several fruits. Some apocarotenoid pigments, such as crocins and bixin, are widely utilized as colorants and additives in food and cosmetic industry and also have health-promoting properties. Considering the importance of this class of metabolites, investigation of apocarotenoid diversity and regulation has increasingly attracted the attention of plant biologists. Here, we provide an update on the plant apocarotenoid biosynthetic pathway, especially highlighting the diversity of the enzyme carotenoid cleavage dioxygenase 4 (CCD4) from different plant species with respect to substrate specificity and regioselectivity, which contribute to the formation of diverse apocarotenoid volatiles and pigments. In addition, we summarize the regulation of apocarotenoid metabolic pathway at transcriptional, post-translational, and epigenetic levels. Finally, we describe inter- and intraspecies variation in apocarotenoid production observed in many important horticulture crops and depict recent progress in elucidating the genetic basis of the natural variation in the composition and amount of apocarotenoids. We propose that the illustration of biochemical, genetic, and evolutionary background of apocarotenoid diversity would not only accelerate the discovery of unknown biosynthetic and regulatory genes of bioactive apocarotenoids but also enable the identification of genetic variation of causal genes for marker-assisted improvement of aroma and color of fruits and vegetables and CRISPR-based next-generation metabolic engineering of high-value apocarotenoids.

3.3.4 Biocatalytic Oxidation of Alcohols: An Overview

This chapter provides a representative, but non-exhaustive, overview of biocatalytic methods for the oxidation of alcohols to the corresponding carbonyl products. Enzymes represent an attractive alternative to established oxidation catalysts, especially if mild reaction conditions are needed or if regio- or stereoselectivity are desirable.

EFFECT OF INSULIN SHOCK ON OXIDATIVE MODIFICATION OF PROTEINS IN THE NERVOUS TISSUE OF THE BRAIN OF LABORATORY RATS

The rationale for the study of the formation of products of oxidative modification of proteins (OMP) in the nervous tissue in an experimental study of the effects of insulin shock was the literature data indicating that, oxidative destruction of proteins is one of the early indicators of tissue damage. The OMP considered as a factor in the pathogenesis of nervous tissue in many diseases. In some studies, there is information about the effect of experimental GP on oxidative processes in blood serum, red blood cells, adrenal glands and some other tissues, but the effect of this pathology on the processes of free radical oxygenation in the nervous tissue not studied. The purpose of this article was to evaluate changes in the level of OMP in the nervous tissue of laboratory rats under the influence of insulin shock. The experiment was performed on 32 sexually mature mongrel male rats weighing 380–400 g (age 6 months), divided into 4 groups of 8 individuals: control (intact) group, group 1-laboratory animals exposed to a single insulin shock (1 time per day, 1 day); group 2 – laboratory rats exposed to a double insulin shock (1 time per day, 2 days); group 3 – laboratory rats exposed to triple exposure to insulin shock (1 time per day, 3 days). Rats of the experimental groups insulin (3.5 Units) subcutaneously were injected. The presence of hypoglycemic coma determined by the appearance of convulsions. Animals that are intact at this time remained in their cells. Experimental animals slaughtered by decapitation on a guillotine. The material for research was a homogenate of nervous tissue obtained by the method Of Kutlubaev M. A. and co-authors. The study of the level of OMB in nervous tissue was performed using the Dubinina E. E. method, based on the reaction of oxidized amino acid residues of protein with 2,4-dinitrophenylhydrazine (2,4 – DNFG) with the formation of anhydrous 2,4 – DNFG. Measurements of supernatant extinction at wavelengths (λ) of 356, 370, 430 and 530 nm performed using a 5400-UV spectrophotometer (Ekros-Analytica, Russia). Statistical processing of the experiment results performed using the student’s parametric t-test, since the experimental data obeyed the law of normal distribution. It was found, that insulin shock and experimental hyperinsulinemia (HI) contributed to a decrease in free radical protein oxidation in rat nervous tissue homogenate, reducing the total level of OMP carbonyl products in all the study groups exposed to insulin shock: in the 1st group – by 37.6 % (n=8; p≤0.01), in the 2nd group – by 40.4 % (n=8; p≤0.01), in the 3rd group – by 40.8 % (n=8; p≤0.01). Experimental HI causes significant changes in the level of OMP products in the nervous tissue of laboratory animals, which expressed in a decrease in aldehyde and ketone derivatives of both the main and neutral characters in comparison with the indicators of the intact group. In all three groups with experimental HI, compared with the intact group, there was a significant decrease in primary and secondary carbonyl products of OMP, which indicates that free radical oxidation processes associated with both fragmentation of protein molecules and their aggregation suppressed under conditions of insulin shock. At one- and three-time exposure to HI, primary markers of oxidative stress, formed mainly due to fragmentation of protein molecules, prevailed among the carbonyl products of OMP in the nervous tissue. The content of primary and secondary carbonyl products was almost equal when the HI applied twice, which indicates that the processes of fragmentation and aggregation of protein molecules were almost the same under these conditions. In all three experimental groups, compared with the intact group, there was a significant decrease in carbonyl products of both neutral and basic nature due to a decrease in free radical damage to neutral and basic amino acids of protein molecules. In all the study groups, including the intact group, the level of OMPo was significantly lower than the level of OMPn. The most pronounced differences between the level of carbonyl products of OMP and OMPo were observed with three-fold HI, and the least pronounced-with a single one. With increasing duration of insulin shock, the spectrum of carbonyl products of OMP shifted towards increasing the content of the main products, as the role of the main amino acids as targets for damage to protein molecules by free radicals increased.

Enhanced Selective Production of Carbonyl Products for Aerobic Oxidation of Benzylic Alcohols over Mesoporous Fe2O3 Supported Gold Nanoparticles

Ordered mesoporous Fe2O3 supported gold nanoparticles with a desired specific surface area and porous structure (Au/meso-Fe2O3) was successfully fabricated with a hard templating method by using KIT-6 as the template. The morphology and physico-chemical properties of Au/meso-Fe2O3 were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM), etc. The gold nanoparticles are highly dispersed on the surface of the mesoporous Fe2O3. The catalytic performance of the synthesized catalyst was studied for the aerobic oxidation of benzylic alcohols in β–O–4 linked lignin model dimers to the corresponding carbonyl products under atmosphere pressure. Au/meso-Fe2O3 shows an enhanced activity for the aerobic oxidation of 1-phenylethanol in comparison with that of Au/bulk-Fe2O3. The promoted catalytic activity is related to the confined porous structure of mesoporous Fe2O3 and more boundaries contact between gold and meso-Fe2O3, which shows that the porous structure of the support has a significant influence on the activity of gold catalysts.

Glycation of Plant Proteins: Regulatory Roles and Interplay with Sugar Signalling?

Glycation can be defined as an array of non-enzymatic post-translational modifications of proteins formed by their interaction with reducing carbohydrates and carbonyl products of their degradation. Initial steps of this process rely on reducing sugars and result in the formation of early glycation products—Amadori and Heyns compounds via Schiff base intermediates, whereas their oxidative degradation or reactions of proteins with α-dicarbonyl compounds yield a heterogeneous group of advanced glycation end products (AGEs). These compounds accompany thermal processing of protein-containing foods and are known to impact on ageing, pathogenesis of diabetes mellitus and Alzheimer’s disease in mammals. Surprisingly, despite high tissue carbohydrate contents, glycation of plant proteins was addressed only recently and its physiological role in plants is still not understood. Therefore, here we summarize and critically discuss the first steps done in the field of plant protein glycation during the last decade. We consider the main features of plant glycated proteome and discuss them in the context of characteristic metabolic background. Further, we address the possible role of protein glycation in plants and consider its probable contribution to protein degradation, methylglyoxal and sugar signalling, as well as interplay with antioxidant defense.

Biomimetic Cu/Nitroxyl Catalyst Systems for Selective Alcohol Oxidation

The oxidation of alcohols to the corresponding carbonyl products is an important organic transformation and the products are used in a variety of applications. The development of catalytic methods for selective alcohol oxidation have garnered significant attention in an attempt to find a more sustainable method without any limitations. Copper, in combination with 2,2,6,6-tetramethyl-1-piperidine N-oxyl (TEMPO) and supported by organic ligands, have emerged as the most effective catalysts for selective alcohol oxidation and these catalyst systems are frequently compared to galactose oxidase (GOase). The efficiency of GOase has led to extensive research to mimic the active sites of these enzymes, leading to a variety of Cu/TEMPO· catalyst systems being reported over the years. The mechanistic pathway by which Cu/TEMPO· catalyst systems operate has been investigated by several research groups, which led to partially contradicting mechanistic description. Due to the disadvantages and limitations of employing TEMPO· as co-catalyst, alternative nitroxyl radicals or in situ formed radicals, as co-catalysts, have been successfully evaluated in alcohol oxidation. Herein we discuss the development and mechanistic elucidation of Cu/TEMPO· catalyst systems as biomimetic alcohol oxidation catalysts.

Gold nanoparticle-functionalized niobium oxide perovskites as photocatalysts for visible light-induced aromatic alcohol oxidations

Spherical gold nanoparticles have been supported onto the surface of potassium niobium oxide perovskites, an underdeveloped class of semiconductor in photocatalytic organic transformations. The nanoparticle dopants of 9.5 nm in diameter and surface plasmon absorption at 530 nm are examined as possible visible light induced catalysts using alcohol photooxidation as the probe reaction. The nanomaterial-induced photooxidation of a series of aromatic alcohols is examined, in the absence of solvent, as a function of base, H2O2, and catalyst concentrations, as well as using multiple visible light sources. This experimental methodology affords extremely selective photooxidation to the carbonyl products (>99%) in as little as 2 h. Using the results obtained from the substitution of the aromatic alcohol, the proposed photocatalytic mechanism is suggested to rely heavily on plasmon-initiated electron transfer from the gold nanoparticle surface to the potassium niobium oxide perovskite and subsequent reductive decomposition of H2O2. This photodegradation step is proposed to favor the formation of ketyl radical species, a key intermediate in the visible light induced mechanism that undergoes both an electron and proton transfer to facilitate formation of the final, carbonyl products. Furthermore, the gold nanoparticle – potassium niobium oxide catalyst exhibits moderate reusability, highly desired in the realm of heterogeneous catalysis.

Marine solids/NaNO3: As Natural and Efficient Catalysts for Aldol condensation

A new and efficient method have been developed for the synthesis of α,β-unsaturated carbonyl compounds from various aldehydes and ketones, using marine calcinated coral/NaNO3 and cuttlebone/NaNO3, as natural and efficient catalysts for cross aldol condensation. The aim of present study was to study the marine solids/NaNO3: as natural and efficient catalyst for Aldol condensation. The materials were purchased from Merck and Aldrich Companies. The IR spectra were recorded on a Perkin-Elmer RXI infrared spectrometer. H NMR spectra were recorded on a 400 MHz Brucker FT-NMR spectrometer. The SEM image was recorded on 1455 VP LEO-Germany. TLC accomplished the purity of substrates and reactions monitored on silica gel (Merck, Germany) Polygram SIGL/UV254 plates. The melting points are uncorrected. Results showed that, the marine solid are efficient catalysts for aldol condensation, but cuttlebone/NaNO3 catalyze this reaction in shorter time (1 hr) than calcinated coral/NaNO3 (6 hr). However, these marine solids have several advantages such as small amount of the catalyst, good absorbent natural solid, easy to handle, and products in good-to-high yields. In conclusion we found marine catalysts, Calcinated Cuttlebone/NaNO3 or Coral/NaNO3 to be an effective catalyst for aldol condensation from ketones having α-hydrogens and aldehydes in 50 % ethanol at reflux conditions. The α,β-unsaturated carbonyl products were obtained in good to high yields. This method offered marked improvement compared to previously reported ones.

Unexpected Pyrolytic Behaviour of Substituted Benzo[c]thiopyran and Thieno[2,3-c]thiopyran S,S-dioxides

Flash vacuum pyrolysis (FVP) of benzo[c]thiopyran S,S-dioxide (1) results in formation of indene and 2-vinylbenzaldehyde as previously described. A range of eight analogues with various substitution patterns are found to behave differently. In general, there is no extrusion of SO2 to give products analogous to indene, but unsaturated carbonyl products analogous to 2-vinylbenzaldehyde are formed in most cases by way of ring expansion to a 7-membered ring sultine, extrusion of SO, and intramolecular hydrogen atom transfer. Other processes observed include formation of anthracene via an isomeric 7-membered sultine with loss of SO, CO and methane or butane, and formation of 4-ethylidene-4,5-dihydrocyclobuta[b]thiophenes by way of SO loss, a radical rearrangement, and extrusion of acetone. The analogues with a halogen substituent at position 8 on the benzene ring require a higher temperature to react and give naphthalene resulting from net elimination of HX and SO2. The X-ray crystal structure of 1 is also reported.