Effect of folic acid supplements on homocysteine concentration in plasma of gestating sows

An experiment comprising 19 German Landrace sows was established to evaluate the effect of folic acid supplements (10 mg/kg concentrate) on homocysteine and folic acid concentration in plasma and serum, respectively, of highly pregnant sows as compared to an unsupplemented control (basal diet contained 0.62 mg folic acid/kg concentrate). Blood samples were taken between day 75 and 110 of gestation for homocysteine analysis and on day 100 of gestation for folic acid determination. Due to the folic acid supplements serum folic acid concentration increased significantly (104 nmol/1 in controls and 140 nmol/1 in supplemented sows). In contrast, homocysteine concentration in the plasma was not significantly influenced by folic acid supplements (16.6 μmol/1 in controls and 15.2 μmol/1 in supplemented sows). Further investigations seem to be necessary to clarify the physiology of homocysteine metabolism in swine.     

Content and deposition of major mineral elements in different tissues and empty body of growing bulls of the german simmental breed

54 bulls of the German Simmental breed were fed either on a high energy level (maize silage ad libitum and 1.8 kg concentrate) or on a low energy level (maize silage restrictively and 1.0 kg concentrate). In dependence on feeding intensity a mean daily weight gain of 870 or 1210 g was obtained. Animals were slaughtered with a live mass of 200 kg, 350 kg, 500 kg, 575 kg and 650 kg. Empty body was divided into 13 cuts and afterwards separated into lean, bone and adipose tissues and tendons. Major mineral element content was determined in these tissues as well as in the noncarcass parts.

In the lean tissue the mean content (200 kg) of 0.3 g calcium, 10 g phosphorus, 1 g magnesium, 2.3 g sodium and 14.8 g potassium/kg dry matter decreased slightly with rising live mass (200–650 kg). The contents of major mineral elements were much higher in bone tissue. For the fattening period from 200 to 650 kg of live mass mean contents of 151.5 g calcium, 71.3 g phosphorus, 3.2 g magnesium, 5.1 g sodium and 1.1 g potassium per kg DM were analysed. Mineral element content of bone tissue increased with rising live mass as well as animals on low feeding intensity showed a higher mineral content than on high energy level. In all, major mineral element content in fat tissue was very low. In noncarcass parts head and legs calcium and phosphorus had analogous to bone tissue the highest concentration. Hide showed a high content of sodium, whereas organs and digestive tract had a high content of potassium and phosphorus. Total mass of major mineral elements in the different tissues increased above all in the fattening period of 200 to 350 kg. In carcass as well as in empty body, mass of calcium and phosphorus was much higher than magnesium, sodium and potassium. Also animals on low feeding intensity showed a higher mass of major mineral elements in carcass and empty body than animals on high energy feeding intensity. The intensively fed bulls had a mean deposition of 12.7 g calcium, 6.9 g phosphorus, 0.37 g magnesium, 1.2 g sodium and 2.1 potassium per 1000 g of empty body weight gain, whereas restrictively fed bulls deposited in average 15.0 g calcium, 7.8 g phosphorus, 0.4 g magnesium, 1.2 g sodium and 2.4 g potassium per 1000 g of empty body weight gain.     

一组人工合成抗菌肽的研究

Cecropin A1是一种从惜古比天蚕(Hyalophora cecropia)中提取的由37个氨基酸组成的一种α-螺旋抗菌肽,其杀菌活性较弱。本文采用了cecropin A1的N端1-8序列KWKLFKKI,另加一段标准的α-螺旋结构序列,然后用一个铰链结构GIG相连,合成了15条抗菌肽。经过试验证明部分含有核心标准螺旋结构的序列,对革兰氏阳性菌和阴性菌的最小抑菌浓度仅是原有cecropin A1抗菌肽的1/100左右。该类抗菌肽有希望进一步开发为新的抗感染药物。该类抗菌肽已经申请专利,专利号为PCT/CN 03/00522。     

Molecular mechanism of antimicrobial peptides: The origin of cooperativity

Based on very extensive studies on four peptides (alamethicin, melittin, magainin and protegrin), we propose a mechanism to explain the cooperativity exhibited by the activities of antimicrobial peptides, namely, a non-linear concentration dependence characterized by a threshold and a rapid rise to saturation as the concentration exceeds the threshold. We first review the structural basis of the mechanism. Experiments showed that peptide binding to lipid bilayers creates two distinct states depending on the bound-peptide to lipid ratio P/L. For P/L below a threshold P/L*, all of the peptide molecules are in the S state that has the following characteristics: (1) there are no pores in the membrane, (2) the axes of helical peptides are oriented parallel to the plane of membrane, and (3) the peptide causes membrane thinning in proportion to P/L. As P/L increases above P/L*, essentially all of the excessive peptide molecules occupy the I state that has the following characteristics: (1) transmembrane pores are detected in the membrane, (2) the axes of helical peptides are perpendicular to the plane of membrane, (3) the membrane thickness remains constant for P/L ≥ P/L*. The free energy based on these two states agrees with the data quantitatively. The free energy also explains why lipids of positive curvature (lysoPC) facilitate and lipids of negative curvature (PE) inhibit pore formation.     

Peptide antibiotics in action: Investigation of polypeptide chains in insoluble environments by rotational-echo double resonance

Rotational-echo double resonance (REDOR) is a solid-state NMR technique that has the capability of providing intra- and intermolecular distance and orientational restraints in non-crystallizable, poorly soluble heterogeneous molecular systems such as cell membranes and cell walls. In this review, we will present two applications of REDOR: the investigation of a magainin-related antimicrobial peptide in lipid bilayers and the study of a vancomycin-like glycopeptide in the cell walls of Staphylococcus aureus.     

Alpha-helical antimicrobial peptides—Using a sequence template to guide structure-activity relationship studies

An important class of cytolytic antimicrobial peptides (AMPs) assumes an amphipathic, α-helical conformation that permits efficient interaction with biological membranes. Host defence peptides of this type are widespread in nature, and numerous synthetic model AMPs have been derived from these or designed de novo based on their characteristics. In this review we provide an overview of the ‘sequence template’ approach which we have used to design potent artificial helical AMPs, to guide structure-activity relationship studies aimed at their optimization, and to help identify novel natural AMP sequences. Combining this approach with the rational use of natural and non-proteinogenic amino acid building blocks has allowed us to probe the individual effects on the peptides' activity of structural and physico-chemical parameters such as the size, propensity for helical structuring, amphipathic hydrophobicity, cationicity, and hydrophobic or polar sector characteristics. These studies furthermore provided useful insights into alternative modes of action for natural membrane-active helical peptides.     

A micellar model system for the role of zeaxanthin in the non-photochemical quenching process of photosynthesis—chlorophyll fluorescence quenching by the xanthophylls

To get an insight to the mechanism of the zeaxanthin-dependent non-photochemical quenching in photosystem II of photosynthesis, we probed the interaction of some xanthophylls with excited chlorophyll-a by trapping both pigments in micelles of triton X-100. Optimal distribution of pigments among micelles was obtained by proper control of the micelle concentration, using formamide in the reaction mixture, which varies the micellar aggregation number over three orders of magnitude. The optimal reaction mixture was obtained around 40% (v/v) formamide in 0.2-0.4% (v/v) triton X-100 in water. Zeaxanthin in the micellar solution exhibited initially absorption and circular dichroism spectral features corresponding to a J-type aggregate. The spectrum was transformed over time (half-time values vary—an average characteristic figure is roughly 20 min) to give features representing an H-type aggregate. The isosbestic point in the series of spectral curves favors the supposition of a rather simple reaction between two pure J and H-types dimeric species. Violaxanthin exhibited immediately stable spectral features corresponding to a mixture of J-type and more predominately H-type dimers. Lutein, neoxanthin and β-carotene did not show any aggregated spectral forms in micelles. The spectral features in micelles were compared to spectra in aqueous acetone, where the assignment to various aggregated types was established previously. The specific tendency of zeaxanthin to form the J-type dimer (or aggregate) could be important for its function in photosynthesis. The abilities of five carotenoids (zeaxanthin, violaxanthin, lutein, neoxanthin and β-carotene) to quench chlorophyll-a fluorescence were compared. Zeaxanthin, in its two micellar dimeric forms, and β-carotene were comparable good quenchers of chlorophyll-a fluorescence. Violaxanthin was a much weaker quencher, if at all. Lutein and neoxanthin rather enhanced the fluorescence. The implications to non-photochemical quenching process in photosynthesis are discussed.     

Investigating molecular recognition and biological function at interfaces using piscidins, antimicrobial peptides from fish

We studied amidated and non-amidated piscidins 1 and 3, amphipathic cationic antimicrobial peptides from fish, to characterize functional and structural similarities and differences between these peptides and better understand the structural motifs involved in biological activity and functional diversity among amidated and non-amidated isoforms. Antimicrobial and hemolytic assays were carried out to assess their potency and toxicity, respectively. Site-specific high-resolution solid-state NMR orientational restraints were obtained from ¹⁵N-labeled amidated and non-amidated piscidins 1 and 3 in the presence of hydrated oriented lipid bilayers. Solid-state NMR and circular dichroism results indicate that the peptides are α-helical and oriented parallel to the membrane surface. This orientation was expected since peptide-lipid interactions are enhanced at the water-bilayer interface for amphipathic cationic antimicrobial peptides. ¹⁵N solid-state NMR performed on oriented samples demonstrate that piscidin experiences fast, large amplitude backbone motions around an axis parallel to the bilayer normal. Under the conditions tested here, piscidin 1 was confirmed to be more antimicrobially potent than piscidin 3 and antimicrobial activity was not affected by amidation. In light of functional and structural similarities between piscidins 1 and 3, we propose that their topology and fast dynamics are related to their mechanism of action.     

Responses of Bradford-reactive soil protein to experimental nitrogen addition in three forest communities in northern lower Michigan

Increased use of anthropogenically fixed N and the release of N in combustion products have led to concerns about possible long-term impacts on terrestrial ecosystems. Previous studies demonstrating the potential of atmospheric N deposition to influence forest soil carbon have focused on decomposition processes with much less known about potential impacts on mycorrhiza-derived carbon. Glomalin is a unique glycoprotein produced by arbuscular mycorrhizal (AM) fungi that has been implicated in the formation of soil aggregates and potentially a significant store of soil carbon. To determine the possible impact of experimental N deposition of such stores we examined the operationally defined glomalin-related soil protein (GRSP) levels over two growing seasons in three forest types receiving background N deposition (control) or treated with 80 kg N ha⁻¹ year⁻¹ as NaNO₃. Three sites of each of three forest types, sugar maple-basswood (SMBW), sugar maple-red oak (SMRO), and black oak-white oak (BOWO), in northern Lower Michigan were studied during the 2001 and 2002 growing seasons. GRSP were extracted from air-dried soils with citric acid and measured by the Bradford method. Analysis of variance revealed significant differences related to forest type and sample date in easily extractable Bradford reactive (EE-BRSP) and Bradford-reactive soil protein (BRSP), but failed to detect significant effects of experimental N amendment. EE-BRSP and BRSP varied in a pattern that was consistent with an AM fungal origin; a pattern that reflected the mycorrhizal types of the dominant over and understory plants of each forest ecosystem. SMBW forests dominated by AM plants had the highest levels of protein. BOWO forests with low AM plant cover had the lowest protein levels and SMRO forests were intermediate. Both Bradford-reactive fractions and their ratio varied seasonally, generally being highest in fall samples. Significant correlations observed between BRSP fractions, phosphorous, and soil organic matter were likely related to covariation of soil properties across forest types. While not statistically significant, response patterns of BRSP to N deposition were ecosystem-specific and reflected mycorrhizal types of dominant species. Abundance of these proteins reflected previously observed changes in SOC in the two forest types examined with abundant AM hosts. Specifically, nitrate addition led to BRSP decreases in SMBW and increases in SMRO forests. Changes in BRSP accounted for a small fraction of the changes in SOC; appearing to increase as a fraction of residual SOC consistent with the idea that GRSP are recalcitrant. BRSP remained unchanged at BOWO sites despite a significant increase in SOC at these sites. Our results point to the potential of proteins as contributors to differential, mycorrhizal type-specific responses to changes in soil carbon following N amendment.     

Litter N:P ratios indicate whether N or P limits the decomposability of graminoid leaf litter

The N:P ratio of leaf litter may determine if decomposability is N-limited (litter with low N:P ratio) or P-limited (litter with high N:P ratio). To test this hypothesis and to determine the threshold between N and P limitation, we studied relationships between litter N and P concentrations, litter mass loss and effects of fertilisation on litter mass loss in laboratory experiments. Leaf litter of 11 graminoid species was collected in Swiss and Dutch wetlands, yielding 84 litter samples with a broad range of N and P concentrations (3.2–15.1 mg N g⁻¹, 0.04–1.93 mg P g⁻¹) and with N:P mass ratios ranging from 5 to 100. On nutrient-free sand, dry mass loss after five or ten weeks (5.5–53% of initial mass) correlated positively with the N and P concentrations of the litter. Within species, mass loss correlated mainly with N for litter with low N:P ratio, and with P for litter with high N:P ratio, in agreement with our hypothesis. Among species, however, these relationships did not exist, and decomposition rather correlated with the specific leaf area. When the litter was incubated on fertilised sand, 35 out of 50 litter samples decomposed faster than on nutrient-free sand. Decomposition was generally accelerated by P fertilisation (i.e. P-limited) when the N:P ratio of the litter was above 25 and the P concentration below 0.22 mg g⁻¹, supporting our hypothesis. N-limited decomposition was not significantly related to the litter N:P ratio but occurred rarely for litter with N:P ratio greater than 25, and only for litter with N concentration below 11.3 mg g⁻¹. We conclude that the N:P ratio of leaf litter indicates whether its decomposability is more likely to be N- or P-limited. The critical N:P ratio (threshold between N and P limitation) appeared to be 25 for graminoid leaf litter.