d-Amino acids in molecular evolution in space – Absolute asymmetric photolysis and synthesis of amino acids by circularly polarized light

Living organisms on the Earth almost exclusively use l-amino acids for the molecular architecture of proteins. The biological occurrence of d-amino acids is rare, although their functions in various organisms are being gradually understood. A possible explanation for the origin of biomolecular homochirality is the delivery of enantioenriched molecules via extraterrestrial bodies, such as asteroids and comets on early Earth. For the asymmetric formation of amino acids and their precursor molecules in interstellar environments, the interaction with circularly polarized photons is considered to have played a potential role in causing chiral asymmetry. In this review, we summarize recent progress in the investigation of chirality transfer from chiral photons to amino acids involving the two major processes of asymmetric photolysis and asymmetric synthesis. We will discuss analytical data on cometary and meteoritic amino acids and their potential impact delivery to the early Earth. The ongoing and future ambitious space missions, Hayabusa2, OSIRIS-REx, ExoMars 2020, and MMX, are scheduled to provide new insights into the chirality of extraterrestrial organic molecules and their potential relation to the terrestrial homochirality. This article is part of a Special Issue entitled: d-Amino acids: biology in the mirror, edited by Dr. Loredano Pollegioni, Dr. Jean-Pierre Mothet and Dr. Molla Gianluca.     

Peroxisomal β-oxidation of fatty acids in bovine and rat liver

Hepatic peroxisomal β-oxidation rates were compared in liver homogenates from cows and rats during different nutritional and physiological states. Peroxisomal oxidation in liver homogenates from cows represented 50% and 77% of the total capacity for the initial cycle of β-oxidation of palmitate and octanoate, respectively, but only 26% and 65% for rats. Lactation or food deprivation did not alter rates of hepatic peroxisomal β-oxidation of palmitate or octanoate in cows. Fasting and clofibrate treatment increased rates of total and peroxisomal β-oxidation of palmitate and octanoate in rat liver.     

Absorption of circularly polarizedγ-radiation in L- and D-amino acids

No difference within the experimental error ( 10³) was observed in the absorption of right- and left-circularly polarized-radiation in L- and D-tryptophan and tyrosine. For the measurements the 14.4 keV transition of⁵⁷Fe was used and the analysis of the circularly polarized-radiation was performed by Mössbauer method.     

Polyunsaturated fatty acids and signalling via phospholipase C-β and A2 in myocardium

Dietary n-6 and n-3 polyunsaturated fatty acids (PUFAs) have potent biological effects on the blood(cells), the vasculature and the myocardium. In the epidemiological studies in which the benefit from the regular ingestion of n-3 PUFAs was reported, the responsible mechanisms remain obscure. A great deal of the PUFA-effect can be explained by the known interference with the eicosanoid metabolism. Many processes, believed to be involved in atherogenesis such as adhesion and infiltration of bloodcells (in)to the vasculature, platelet aggregation, secretion of endothelium-derived factors and mitogenic responses of vascular smooth muscle cells are partially mediated by receptor-activated phospholipases C- and A₂. As PUFAs take part at many steps of the signalling pathways, the latter could represent important action sites to beneficially interfere with atherogenesis. In this brief review, we have discussed the results of studies on the influence of alteration of PUFA composition of the membrane phospholipids or of exogenously administered non-esterified PUFAs on phospholipid signalling. For convenience, we have mainly focused our discussion on those studies available on the myocardium. By changing the PUFA composition of the phospholipids, the endogenous substrates for the membrane-associated phospholipase C- and A₂ are changed. This is accompanied by changes in their hydrolytic action on these substrates resulting in altered products (the molecular species of 1,2-diacylglycerols and the non-esterified PUFAs) which on their turn evoke changes in events downstream of the signalling cascades: activation of distinct protein kinase C isoenzymes, formation of distinct eicosanoids and non-esterified PUFA effects on Ca ²⁺ channels. It has also become more clear that the membrane physicochemical properties, in terms of fluidity and cholesterol content of the bilayer, might undergo changes due to altered PUFA incorporation into the membrane phospholipids. The latter effects could have consequences for the receptor functioning, receptor-GTP-binding protein coupling, GTP-binding protein-phospholipase C- or A₂ coupling as well. It should be noted that most of these studies have been carried out with cardiomyocytes isolated from hearts of animals on PUFA diet or incubation of cultured cardiomyocytes with non-esterified PUFAs in the presence of albumin. Studies need to be performed to prove that the PUFA-diet induced modulations of the phospholipid signalling reactions do occur in vivo and that these effects are involved in the mechanism of beneficial effects of dietary PUFAs on the process of atherosclerosis.     

Free amino acids and γ-glutamyl peptides in seeds of Fagus silvatica

The contents of amino acids and peptides have been investigated in seeds of Fagus silvatica L. (beechnuts). In addition to the common amino acids, the following compounds have been isolated and identified: 4-hydroxyproline (probably the cis-l-isomer), N⁵-acetylornithine, 3-(2-furoyl)-l-alanine, methionine sulfoxide (probably an artefact), pipecolic acid (probably partially racemized d-isomer), l-willardiine (with a small amount of the d-isomer), N-(3-amino-3-carboxypropyl)azetidine-2-carboxylic acid, N-[N-(3-amino-3-carboxypropyl)-3-amino-3-carboxypropyl]azetidine-2-carboxylic acid, 2(S),5(S),6(S)-5-hydroxy-6-methylpipecolic acid, 2(S),5(R),6(S)-5-hydroxy-6-methylpipecolic acid, γ-glutamylalanine, γ-glutamylglutamic acid, γ-glutamylisoleucine, γ-glutamylleucine, γ-glutamylmethionine sulfoxide (probably an artefact), γ-glutamylphenylalanine, γ-glutamyltyrosine, γ-glutamylvaline, glutathione, γ-glutamylwillardiine, and γ-glutamylphenylalanylwillardiine. γ-Glutamylphenylalanine and willardiine are the dominating components of the amino acid fraction.The isolations were performed by use of ion exchange chromatography, taking advantage of the different pK-values of the amino acids, mainly on acid resins in the 3-chloropyridinium form with aq. 3-chloropyridine as eluant and on basic resins in the acetate form with aqueous acetic acid as eluant. These methods in combination with preparative paper chromatography have permitted the isolation and identification of compounds present in amounts as low as 1/6000 of the dominant ninhydrin-reactive component. The implications of the occurrence of this large variety of compounds in the Fagaceae are briefly discussed.     

Changes in intracellular and extracellular α-amino acids in Gloeothece during N2-fixation and following addition of ammonium

Changes in extracellular and intracellular free amino acids were followed during cyclic phases of N₂-fixation (acetylene reduction) by cultures of the axenic, non-heterocystous cyanobacterium Gloeothece incubated under alternating light and darkness or continuous illumination. Changes in intracellular amino acids were minor, with only arginine (increasing during N₂-fixation) and glutamate (decreasing during fixation) showing significant changes in cells incubated under 12 h light: 12 h dark. The intracellular concentration of glutamine in cultures was always very low and the value of the ratio glutamine: glutamate (GLN:GLU), used as an index of C–N status in eukaryote microbes, was consistently less than 0.05 suggesting that the cells were nitrogen-stressed. On addition of ammonium, there was a transient accumulation of intracellular glutamine, and the ratio GLN:GLU increased rapidly to a value greater than 0.5, typical of unstressed eukaryotes. In contrast to intracellular amino acids, there were significant changes in extracellular amino acids in cultures incubated under alternating light and darkness. Glycine, serine and alanine were released during the dark phase and were taken up again in the light, paralleling the diurnal pattern of nitrogenase activity (high in darkness). It is postulated that this release is usually retained in the mucilage surrounding the cells (but disturbed during even gentle filtration) and that this mucilage may constitute an extracellular vacuole.     

A preparation of N-Fmoc-N-methyl-α-amino acids and N-nosyl-N-methyl-α-amino acids

A convenient route for the synthesis of lipophilic N-Fmoc-N-methyl-α-amino acids and N-nosyl-N-methyl-α-amino acids, interesting building blocks to be used for the preparation of N-methylated peptides, is presented. Both nosyl- and Fmoc-protected monomers are accessible, so these compounds can be used in solution as well as in solid phase peptide synthesis. The methodology is based on the use of benzhydryl group to protect temporarily the carboxyl function of N-nosyl-α-amino acids and on the subsequent methylation of the N-nosyl-α-amino acid benzhydryl esters with diazomethane. The benzhydryl esters offer several beneficial features such as simple preparation, stability to methylation and selective deprotection under mild conditions. The overall procedure is highly efficient in that the adopted conditions keep the chiral integrity of amino acid precursors and the process does not require chromatographic purification of the methylated products.     

Effects ofγ-irradiation on embryonic development and nucleic acids in trigeminal neurons

Summary Pregnant rats were exposed to absorbed doses of 0.5, 1, 2, and 4 Gy of⁶⁰Co- rays either on day 8 or on day 12 p.c.. The embryos were collected on day 18 p.c.. Irradiations both on day 8 and 12 p.c. result in a dose dependent decrement of weight. The effect is larger for irradiation on day 8 p.c.. Caryometric studies of the neurons in the trigeminal ganglion show, on the other hand, that the reduction of nuclear sizes in this tissue is more substantial for an irradiation on day 12 p.c. when the ganglion is in a stage of formation. Cytophotometric determinations of the Feulgen-DNA content and determination of the RNA content by staining with chromic gallocyanin in combination with ribonuclease digestion lead to the conclusion that the irradiation induces no significant hyperploidy and that the irradiated neurons have the nuclear RNA content that is normal at this stage of gestation. This applies both to the irradiations on day 8 and on day 12 p.c.     

Differences in circadian time course and level for the plasma concentrations of glucose,free fatty acids and amino acids between ad lib‐eating and fasting rabbits

Abstract

The entrained rhythm in food approaches, representative of the circadian fluctuation in locomotor and food intake activity was recorded from 12 rabbits eating ad libitum during exposure to an LD 12:12 h‐regimen. They were also subjected to 53 h‐sessions with the same LD alternation, in which blood samples were taken at 2 h‐intervals. During these sessions 6 of them were permitted to eat freely whereas the others were food‐deprived. It appeared that in eating rabbits plasma levels are higher for glucose and a‐amino nitrogen but lower for free fatty acids and, further, that eating specimens exhibit marked circadian fluctuations in the levels of glucose and FFA which are closely correlated with, and probably a consequence of, the circadian rhythm in the amounts of food actually taken up in the course of the sessions. In fasting rabbits, however, the same plasma parameters show rhythms with quite another time course, that can be attributed to the circadian fluctuations in (locomotor) activity and endocrine balance.     

β-Glucan extracts inhibit the in vitro intestinal uptake of long-chain fatty acids and cholesterol and down-regulate genes involved in lipogenesis and lipid transport in rats

BackgroundDietary fiber reduces the intestinal absorption of nutrients and the blood concentrations of cholesterol and triglycerides.AimWe wished to test the hypothesis that high-viscosity (HV) and low-viscosity preparations of barley and oat β-glucan modify the expression of selected genes of lipid-binding proteins in the intestinal mucosa and reduce the intestinal in vitro uptake of lipids.MethodsFive different β-glucan extracts were separately added to test solutions at concentrations of 0.1–0.5% (wt/wt), and the in vitro intestinal uptake of lipids into the intestine of rats was assessed. An intestinal cell line was used to determine the effect of β-glucan extracts on the expression of intestinal genes involved in lipid metabolism and fatty acid transport.ResultsAll extracts reduced the uptake of 18:2 when the effective resistance of the unstirred water layer was high. When the unstirred layer resistance was low, the HV oat β-glucan extract reduced jejunal 18:2 uptake, while most extracts reduced ileal 18:2 uptake. Ileal 18:0 uptake was reduced by the HV barley extract, while both jejunal and ileal cholesterol uptakes were reduced by the medium-purity HV barley extract. The inhibitory effect of HV barley β-glucan on 18:0 and 18:2 uptake was more pronounced at higher fatty acid concentrations. The expression of genes involved in fatty acid synthesis and cholesterol metabolism was down-regulated with the HV β-glucan extracts. β-Glucan extracts also reduced intestinal fatty-acid-binding protein and fatty acid transport protein 4 mRNA.ConclusionsThe reduced intestinal fatty acid uptake observed with β-glucan is associated with inhibition of genes regulating intestinal uptake and synthesis of lipids. The inhibitory effect of β-glucan on intestinal lipid uptake raises the possibility of their selective use to reduce their intestinal absorption.     

Associations between peripartum lying and activity behaviour and blood non-esterified fatty acids and β-hydroxybutyrate in grazing dairy cows

During early lactation, most dairy cows experience negative energy balance (NEB). Failure to cope with this NEB, however, can place cows at greater risk of developing metabolic disease. Our objective was to characterise, retrospectively, lying behaviour and activity of grazing dairy cows grouped according to blood non-esterified fatty acids (NEFAs) and β-hydroxybutyrate (BHB) as indicators of postpartum metabolic state. Blood was sampled weekly for up to 4 weeks precalving, on the day of calving (day 0), daily between 1 and 4 days postcalving, and then at least weekly between week 1 and week 5 postcalving for analysis of plasma NEFAs and BHB concentrations. Two hundred and forty-four multiparous Holstein-Friesian and Holstein-Friesian × Jersey cows were classified into one of three metabolic status groups based on maximum blood NEFAs and BHB concentrations during week 1 and 2 postcalving. A cow was classified as having either: (1) low NEFAs and low BHB (Lo–Lo; n = 78), when all blood samples were <1.0 mmol/L for NEFAs and ≤1.0 mmol/L for BHB during the first 2 weeks postcalving; (2) high NEFAs and low BHB (Hi–Lo; n = 134), when blood NEFAs were ≥1.0 mmol/L and blood BHB was ≤1.0 mmol/L at the same sampling time point during the first 2 weeks postcalving; or (3) high NEFAs and high BHB (Hi–Hi; n = 32), when blood NEFAs were ≥1.0 mmol/L and blood BHB was ≥1.2 mmol/L at the same sampling time point during the first 2 weeks postcalving. Accelerometers (IceTag or IceQube devices; IceRobotics Ltd.) were used to monitor lying and activity behaviours peripartum (–21 to +35 days relative to calving). Changes in lying behaviour and activity occurred before the mean day that cows were classified Hi–Hi and Hi–Lo (2.2 and 3.5 d postcalving, respectively). Up to 3 weeks preceding calving, Hi–Hi cows were more active, had fewer daily lying bouts (LBs), and spent less time lying than Lo–Lo cows. In addition, Hi–Hi cows had fewer daily LBs and were less active up to 4 weeks postcalving than Lo–Lo cows, but these differences were biologically small. Groups of grazing cows classified as experiencing a more severe metabolic challenge behave differently up to 3 weeks precalving than their herdmates with lower blood NEFAs and BHB postcalving. These altered behaviours may allow identification of individual cows at risk of a metabolic challenge, but further research is required.     

Alicyclic β-amino acids in Medicinal Chemistry

Summary. The structural element of alicyclic β-amino acids shows some remarkable biological effects: For some 5- and 6-membered β-amino acids a unique anti fungal activity has been observed, 7-membered β-amino acid derivatives have been investigated for neurological disorders. The application of 5-, 6- and 7-membered alicyclic β-amino acids in Medicinal Chemistry will be reported.     

Critical amino acids in human DNA polymerases η and κ involved in erroneous incorporation of oxidized nucleotides

Oxidized DNA precursors can cause mutagenesis and carcinogenesis when they are incorporated into the genome. Some human Y-family DNA polymerases (Pols) can effectively incorporate 8-oxo-dGTP, an oxidized form of dGTP, into a position opposite a template dA. This inappropriate G:A pairing may lead to transversions of A to C. To gain insight into the mechanisms underlying erroneous nucleotide incorporation, we changed amino acids in human Polη and Polκ proteins that might modulate their specificity for incorporating 8-oxo-dGTP into DNA. We found that Arg61 in Polη was crucial for erroneous nucleotide incorporation. When Arg61 was substituted with lysine (R61K), the ratio of pairing of dA to 8-oxo-dGTP compared to pairing of dC was reduced from 660:1 (wild-type Polη) to 7 : 1 (R61K). Similarly, Tyr112 in Polκ was crucial for erroneous nucleotide incorporation. When Tyr112 was substituted with alanine (Y112A), the ratio of pairing was reduced from 11: 1 (wild-type Polκ) to almost 1: 1 (Y112A). Interestingly, substitution at the corresponding position in Polη, i.e. Phe18 to alanine, did not alter the specificity. These results suggested that amino acids at distinct positions in the active sites of Polη and Polκ might enhance 8-oxo-dGTP to favor the syn conformation, and thus direct its misincorporation into DNA.     

Measurement of eight scalar and dipolar couplings for methine–methylene pairs in proteins and nucleic acids

A new 3D, spin-state-selective coherence transfer NMR experiment is described that yields accurate measurements for eight scalar or dipolar couplings within a spin system composed of a methylene adjacent to a methine group. Implementations of the experiment have been optimized for proteins and for nucleic acids. The experiments are demonstrated for C–C moieties of the third IgG-binding domain from Streptococcal Protein G (GB3) and for C –C groups in a 24-nt RNA oligomer. Chemical shifts of C, C and H (respectively C , C and H ) are dispersed in the three orthogonal dimensions, and the absence of heteronuclear decoupling leads to distinct and well-resolved E.COSY multiplet patterns. In an isotropic sample, the E.COSY displacements correspond to ¹J_CH, ²J_CH2+²J_CH3, ²J_CH, ¹J_CH2+¹J_CH3, ¹J_CH2–²J_H2H3, ¹J_CH3–²J_H2H3, ³J_HH2 and ³J_HH3 for proteins, and ¹J , ²J J , ²J , ¹J +¹J , ¹J J , ¹J J , ³J and ³J in nucleic acids. The experiment, based on relaxation-optimized spectroscopy, yields best results when applied to residues where the methine–methylene group corresponds to a reasonably isolated spin system, as applies for C, F, Y, W, D, N and H residues in proteins, or the C –C groups in nucleic acids. Splittings can be measured under either isotropic or weakly aligned conditions, yielding valuable structural information both through the ³J couplings and the one-, two- and three-bond dipolar interactions. Dipolar couplings for 10 out of 13 sidechains in GB3 are found to be in excellent agreement with its X-ray structure, whereas one residue adopts a different backbone geometry, and two residues are subject to extensive ₁ rotamer averaging. The abundance of dipolar couplings can also yield stereospecific assignments of the non-equivalent methylene protons. For the RNA oligomer, dipolar data yielded stereospecific assignments for six out of the eight C H₂ groups in the loop region of the oligomer, in all cases confirmed by ¹J ^{1} $$" align="middle" border="0"> J , and H resonating downfield of H .Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1007/s10858-005-0175-z.     

Higher de novo synthesized fatty acids and lower ω3- and ω6-long-chain polyunsaturated fatty acids in umbilical vessels of women with preeclampsia and high fish intakes

Umbilical veins (UV) and arteries (UA) of preeclamptic women in Curaçao harbor lower long-chain polyunsaturated fatty acids (LCP). The present aim was to test these findings in Mwanza (Tanzania), whose inhabitants have high LCPω3 and LCPω6 intakes from Lake Victoria fish. Women with preeclampsia (n=28) in Mwanza had lower PUFA and higher 20:0 in UV and UA, compared with normotensive/non-proteinuric controls (n=31). Their UV 22:6ω3, 22:4ω6, LCPω6, ω6, and LCPω3+ω6 were lower, while saturated FA, potentially de novo synthesized FA (Σde novo) and (Σde novo)/(LCPω3+ω6) ratio were higher. Their UA had higher 16:1ω7, ω7, 18:0, and 16:1ω7/16:0. Umbilical vessels in Mwanza had higher 22:6ω3, LCPω3, ω3, and 16:0, and lower 22:5ω6, 20:2ω6, 18:1ω9, and ω9, compared to those in Curaçao. Preeclampsia in both Mwanza and Curaçao is characterized by lower LCP and higher Σde novo. An explanation of this might be placental dysfunction, while the similarity of umbilical vessel FA-abnormalities in preeclamptic and diabetic pregnancies suggests insulin resistance as a common denominator.     

Alterations in synaptosomal neurotransmitter amino acids in “petit-mal” rats at a daytime and a nighttime

The synaptosoma fractions of 6 brain areas-olfactory tubercles (OT), frontal cortex (FC), striatum (Sr), amygdala (A), thalamus (Th), hypothalamus (Hy)-have been analyzed for their neurotransmitter amino acids (AA) content in Wistar rats exhibiting petit-mal epilepsy (PM-E) and in controls (C). The analysis was carried out at 11 p.m. (nighttime corresponding to the acrophase for the hourly number of spike-wave complexes) and at 11 a.m. (daytime). A day versus night rhythmicity is recorded for synaptosomal inhibitory AA in control and in PM-E rats. However, day versus night variations are more frequent and more prominent in C rats than in PM-E rats. Two day versus night variations exist only in PM-E rats: increases of GABA level in Sr and of Asp in Hy. Differences between PME-and C in synaptosomal AA content are more likely to be present during the nighttime. During this period lower AA values for PM-E rats are found for one or several inhibitory AA in OT, Th, and FC. It seems that the differences between PM-E and C concerning the inhibitory AA correlate with the number of spike-wave discharges. Only in one brain area is there a similar difference for PM-E and C during daytime and nighttime: a decreased GABA content for PM-E rats in OT. The decrease is larger in nighttime than in daytime. This difference may serve as a marker for this epileptic disorder. Moreover, it is in OT that the greatest number of PM-E versus C differences in synaptosomal neurotransmitter AA are observed. In view of these and former data, the existence of different alterations in synaptosomal neurotransmitter AA for different types of epilepsy is suggested.Abbreviations used GABA 4-aminobutyrate - Tau taurine - Gly glycine - Asp aspartate - Glu glutamate - Gln glutamine - OT offactory tubereles - FC fronto-parietal cortex - Sr striatum - A amygdala - Th lateral thalamus - Hy lateral hypothalamus - AA neurotransmitter amino acids - I inhibitory - E excitatory - C control rats - PM-E petit-mal rats