Mechanical asymmetry during articulation of tibial and femoral cartilages: Local and overall compressive and shear deformation and properties

During knee movement, femoral cartilage articulates against cartilage from the tibial plateau, and the resulting mechanical behavior is yet to be fully characterized. The objectives of this study were to determine (1) the overall and depth-varying axial and shear strains and (2) the associated moduli, of femoral and tibial cartilages during the compression and shearing of apposing tibial and femoral samples. Osteochondral blocks from human femoral condyles (FCs) characterized as normal and donor-matched lateral tibial plateau (TP) were apposed, compressed 13%, and subjected to relative lateral motion. When surfaces began to slide, axial (?E_zz) and shear (E_xz) strains and compressive (E) and shear (G) moduli, overall and as a function of depth, were determined for femoral and tibial cartilages. Tibial ?E_zz was ～2-fold greater than FC ?E_zz near the surface (0.38 versus 0.22) and overall (0.16 versus 0.07). Near the surface, E_xz of TP was 8-fold higher than that of FC (0.41 versus 0.05), while overall E_xz was 4-fold higher (0.09 versus 0.02). For TP and FC, ?E_zz and E_xz were greatest near the surface and decreased monotonically with depth. E for FC was 1.7-fold greater than TP, both near the surface (0.40 versus 0.24 MPa) and overall (0.76 versus 0.47 MPa). Similarly, G was 7-fold greater for FC (0.22 MPa) than TP near the surface (0.03 MPa) and 3-fold higher for FC (0.38 MPa) than TP (0.13 MPa) overall. These results indicate that tibial cartilage deforms and strains more axially and in shear than the apposing femoral cartilage during tibial–femoral articulation, reflecting their respective moduli.     

The tyrosinase inhibitory effects of isoxazolone derivatives with a (Z)-β-phenyl-α, β-unsaturated carbonyl scaffold

Thirteen (Z)-4-(substituted benzylidene)-3-phenylisoxazol-5(4H)-ones were designed to confirm the geometric effect of the double bond of the β-phenyl-α, β-unsaturated carbonyl scaffold on tyrosinase inhibitory activity. Compounds 1a–1m, which all possessed the (Z)-β-phenyl-α, β-unsaturated carbonyl scaffold, were synthesized using a tandem reaction consisting of an isoxazolone ring formation and a Knoevenagel condensation, and three starting materials, ethyl benzoylacetate, hydroxylamine and benzaldehydes. Some of the compounds showed inhibitory activity against mushroom tyrosinase as potent as compounds containing the “(E)”-β-phenyl-α, β-unsaturated carbonyl scaffold. Compounds 1c and 1m showed greater inhibitory activity than kojic acid: IC₅₀?=?32.08?±?2.25?μM for 1c; IC₅₀?=?14.62?±?1.38?μM for 1m; and IC₅₀?=?37.86?±?2.21?μM for kojic acid. A kinetic study indicated that 1m inhibited tyrosinase in a competitive manner and that it probably binds to the enzyme’s active site. In silico docking simulation supported binding of 1m (?7.6?kcal/mol) to the active site of tyrosinase with stronger affinity than kojic acid (?5.7?kcal/mol). Similar results were obtained using cell-based assays, and in B16F10 cells, compound 1m dose-dependently inhibited tyrosinase activity and melanogenesis. These results indicate the anti-melanogenic effect of compound 1m is due to the inhibition of tyrosinase and (Z)-isomer of the β-phenyl-α, β-unsaturated carbonyl scaffold can, like its congener the (E)-isomer, act as an excellent scaffold for tyrosinase inhibition.     

Voltage clamp studies of fertilization in sea urchin eggs: I. Effect of clamped membrane potential on sperm entry,activation, and development

To analyze the role of the activation potential (a positive shift of the membrane potential which occurs following sperm attachment) in fertilization and development of the sea urchin egg, unfertilized Lytechinus variegatus eggs were voltage clamped at membrane potentials (E_m) from +20 to ?90 mV, and then inseminated. Either a fast two electrode voltage clamp, or a single electrode switched voltage clamp was used. The clamp was maintained for 3 to 15 min after initiation of a conductance increase. At E_m more positive than +18 mV, even though many sperm may attach, the egg remains completely inert (Jaffe, Nature (London)261, 68–71, 1976). At E_m from +17 to ?90 mV, all inseminated eggs elevate normal fertilization envelopes, although substantially increased concentrations of sperm are required at E_m from +17 to +12 mV. Whether cleavage occurs depends on the clamped E_m. When clamped at E_m from +17 to ?25 mV, 100% of activated eggs cleave. However, when clamped at E_m from ?26 to ?75 mV the percentage of activated eggs which cleave progressively decreases. At clamped E_m between ?76 and ?90 mV, none of the activated eggs cleave. All monospermic voltage clamped eggs that cleave develop to normal swimming blastulae. In all eggs that fail to cleave (clamped at E_m more negative than ?30 mV), sperm penetration is blocked, the sperm is lifted off the egg surface as the fertilization envelope rises, and a sperm aster never forms. Preventing formation of the fertilization envelope by prior disruption of the vitelline layer with dithiothreitol does not promote entry of the sperm. In conclusion, preventing the depolarization normally associated with fertilization suppresses sperm entry in the sea urchin egg, yet activation proceeds. Present evidence suggests an effect of the electrical field across the plasma membrane in suppressing sperm entry.     

Changes in membrane potential during mouse egg development

The electrical membrane potential (E_m) was measured in the developing mouse egg with intracellular microelectrodes. The oocyte had a low negative E_m of ?8.3 ± 0.8 mV (mean ± SE) when immature, which decreased and reversed polarity to a small positive value (+1.9 ± 0.2 mV) in the mature ovulated oocyte. After fertilization E_m returned to a negative value (?9.2 ± 0.5 mV) similar in magnitude to that observed in immature oocytes and then increased significantly (P < 0.01) at both the two-cell (?10.7 ± 0.3 mV) and morula stage (?12.8 ± 0.7 mV) and leveled out at the blastocyst stage (?12.9 ± 0.7 mV). Average potential difference recorded across the blastocoele wall of not fully expanded blastocysts was ?5.0 ± 0.5 mV. These data represent the first report on membrane potentials of the mammalian egg during development. A striking similarity is seen in the relative changes in E_m throughout development of the mouse egg in comparison to those seen in other invertebrate and vertebrate eggs.     

Osthenol,a prenylated coumarin,as a monoamine oxidase A inhibitor with high selectivity

Osthenol (6), a prenylated coumarin isolated from the dried roots of Angelica pubescens, potently and selectively inhibited recombinant human monoamine oxidase-A (hMAO-A) with an IC₅₀ value of 0.74?µM and showed a high selectivity index (SI?>?81.1) for hMAO-A versus hMAO-B. Compound 6 was a reversible competitive hMAO-A inhibitor (K_i?=?0.26?µM) with a potency greater than toloxatone (IC₅₀?=?0.93?µM), a marketed drug. Isopsoralen (3) and bakuchicin (1), furanocoumarin derivatives isolated from Psoralea corylifolia L., showed slightly higher IC₅₀ values (0.88 and 1.78?µM, respectively) for hMAO-A than 6, but had low SI values (3.1 for both). Other coumarins tested did not effectively inhibit hMAO-A or hMAO-B. A structural comparison suggested that the 8-(3,3-dimethylallyl) group of 6 increased its inhibitory activity against hMAO-A compared with the 6-methoxy group of scopoletin (4). Molecular docking simulations revealed that the binding affinity of 6 for hMAO-A (?8.5?kcal/mol) was greater than that for hMAO-B (?5.6?kcal/mol) and that of 4 for hMAO-A (?7.3?kcal/mol). Docking simulations also implied that 6 interacted with hMAO-A at Phe208 and with hMAO-B at Ile199 by carbon hydrogen bondings. Our findings suggest that osthenol, derived from natural products, is a selective and potent reversible inhibitor of MAO-A, and can be regarded a potential lead compound for the design of novel reversible MAO-A inhibitors.     

Design and discovery of thioether and nicotinamide containing sorafenib analogues as multikinase inhibitors targeting B-Raf,B-RafV600E and VEGFR-2

New sorafenib derivatives containing thioether and nicotinamide moiety were designed and synthesized as B-Raf, B-Raf^V600E and VEGFR-2 multikinase inhibitors. Their in vitro enzymatic inhibitory activities against B-Raf, B-Raf^V600E and VEGFR-2 and their antiproliferative activities against HCT-116 and B16BL6 cell lines were evaluated and described. Most of the compounds showed potent activities against both cell lines and specific kinases. Compounds a1, b1 and c4, which exhibited the most potent inhibitory activities against B-Raf with IC₅₀ of 21?nM, 27?nM and 17?nM, B-Raf^V600E with IC₅₀ of 29?nM, 28?nM and 16?nM, VEGFR-2 with IC₅₀ of 84?nM, 46?nM and 63?nM, respectively, and good antiproliferative activities, also demonstrated competitive antiangiogenic activities to sorafenib in in vitro HUVEC tube formation assay.     

Synthesis and evaluation of Re/99mTc(I) complexes bearing a somatostatin receptor-targeting antagonist and labeled via a novel [N,S,O] clickable bifunctional chelating agent

The somatostatin receptor subtype 2 (SSTR2) is often highly expressed on neuroendocrine tumors (NETs), making it a popular in vivo target for diagnostic and therapeutic approaches aimed toward management of NETs. In this work, an antagonist peptide (sst₂-ANT) with high affinity for SSTR2 was modified at the N-terminus with a novel [N,S,O] bifunctional chelator (2) designed for tridentate chelation of rhenium(I) and technetium(I) tricarbonyl cores, [Re(CO)₃]⁺ and [^99mTc][Tc(CO)₃]⁺. The chelator-peptide conjugation was performed via a Cu(I)-assisted click reaction of the alkyne-bearing chelator (2) with an azide-functionalized sst₂-ANT peptide (3), to yield NSO-sst₂-ANT (4). Two synthetic methods were used to prepare Re-4 at the macroscopic scale, which differed based on the relative timing of the click conjugation to the [Re(CO)₃]⁺ complexation by 2. The resulting products demonstrated the expected molecular mass and nanomolar in vitro SSTR2 affinity (IC₅₀ values under 30?nM, AR42J cells, [¹²⁵I]iodo-Tyr¹¹-somatostatin-14 radioligand standard). However, a difference in their HPLC retention times suggested a difference in metal coordination modes, which was attributed to a competing N-triazole donor ligand formed during click conjugation. Surprisingly, the radiotracer scale reaction of [^99mTc][Tc(OH₂)₃(CO)₃]⁺ (^99mTc; t_½?=?6?h, 141?keV γ) with 4 formed a third product, distinct from the Re analogues, making this one of the unusual cases in which Re and Tc chemistries are not well matched. Nevertheless, the [^99mTc]Tc-4 product demonstrated excellent in vitro stability to challenges by cysteine and histidine (≥98% intact through 24?h), along with 75% stability in mouse serum through 4?h. In vivo biodistribution and microSPECT/CT imaging studies performed in AR42J tumor-bearing mice revealed improved clearance of this radiotracer in comparison to a similar [^99mTc][Tc(CO)₃]-labeled sst₂-ANT derivative previously studied. Yet despite having adequate tumor uptake at 1?h (4.9% ID/g), tumor uptake was not blocked by co-administration of a receptor-saturating dose of SS-14. Aimed toward realignment of the Re and Tc product structures, future efforts should include distancing the alkyne group from the intended donor atoms of the chelator, to reduce the coordination options available to the [M(CO)₃]⁺ core (M?=?Re, ^99mTc) by disfavoring involvement of the N-triazole.     

Discovery,design, and synthesis of anti-metastatic lead phenylmethylene hydantoins inspired by marine natural products

The Red Sea sponge Hemimycale arabica afforded the known (Z)-5-(4-hydroxybenzylidene)-hydantoin (1), (R)-5-(4-hydroxybenzyl)hydantoin (2), and (Z)-5-((6-bromo-1H-indol-3-yl)methylene)-hydantoin (3). The natural phenylmethylene hydantoin (PMH) 1 and the synthetic (Z)-5-(4-(ethylthio)benzylidene)-hydantoin (4) showed potent in vitro anti-growth and anti-invasive properties against PC-3M prostate cancer cells in MTT and spheroid disaggregation assays. PMHs 1 and 4 also showed significant anti-invasive activities in orthotopic xenograft and transgenic mice models. To study the effect of electronic and lipophilic parameters on the activity, a wide array of several substituted aldehydes possessing electron-withdrawing (+σ), lipophilic (+π), electron-donating (?σ), and less lipophilic substituents (?π) were used to synthesize several PMHs. Few des-phenylmethylenehydantoins and 2-thiohydanoins were also synthesized and the anti-invasive activities of all compounds were evaluated. Comparative molecular field analysis (CoMFA) was then used to study the 3D QSAR. Predictive 3D QSAR model with conventional r² and cross validated coefficient (q²) values up to 0.910 and 0.651 were established. In conclusion, PMH is a novel antimetastatic lead class with potential to control metastatic prostate cancer.     

Mechanosensitive ion channels in chara: influence of water channel inhibitors, HgCl2 and ZnCl2, on generation of receptor potential

Characean internodal cells generate receptor potential (ΔE _m) in response to mechanical stimuli. Upon a long-lasting stimulus, the cells generated ΔE _m at the moment of both compression and decompression, and the amplitude of ΔE _m at the moment of decompression, (ΔE _m)_E, was larger than that at compression. The long-lasting stimulus caused a membrane deformation (ΔD _m) having two components, a rapid one, (ΔD _m)_rapid, at the moment of compression and a slower one, (ΔD _m)_slow, during the long-lasting compression. We assumed that (ΔD _m)_slow might have some causal relation with the larger ΔE _m at (ΔE _m)_E. We treated internodal cells with either HgCl₂ or ZnCl₂, water channel inhibitors, to decrease (ΔD _m)_slow. Both inhibitors attenuated (ΔD _m)_slow during compression. Cells treated with HgCl₂ generated smaller (ΔE _m)_E compared to nontreated cells. On the other hand, cells treated with ZnCl₂ never attenuated (ΔE _m)_E but, rather, amplified it. Thus, the amplitude of (ΔD _m)_slow did not always show tight correlation with the amplitude of (ΔE _m)_E. Furthermore, when a constant deformation was applied to an internodal cell in a medium with higher or lower osmotic value, a cell having higher turgor always showed a larger (ΔE _m)_E. Thus, we concluded that changes in tension at the membrane may be the most important factor to induce activation of mechanosensitive Ca²⁺ channel.     

Design,synthesis, 3D pharmacophore,QSAR, and docking studies of carboxylic acid derivatives as Histone Deacetylase inhibitors and cytotoxic agents

In this study, five series of (E)-6-(4-substituted phenyl)-4-oxohex-5-enoic acids IIb–f (E), (E)-3-(4-(substituted)-phenyl)acrylic acids IIIa–g (E), 4-(4-(substituted)phenylamino)-4-oxobutanoic acids VIa,b,e, 5-(4-(substituted)phenylamino)-5-oxopentanoic acids VIIa,f and 2-[(4-(substituted)phenyl) carbamoyl]benzoic acids VIIIa,e were designed and synthesized. Selected compounds were screened in vitro for their cytotoxic effect on 60 human NCI tumor cell lines. Compound IIf (E) displayed significant inhibitory activity against NCI Non-Small Cell Lung A549/ATCC Cancer cell line (68% inhibition) and NCI-H460 Cancer cell line (66% inhibition). Moreover, the final compounds were evaluated in vitro for their cytotoxic activity on HepG2 Cancer cell line in which histone deacetylase (HDAC) is overexpressed. Compounds IIc (E), IIf (E), IIIb (E), and IIIg (E) exhibited the highest cytotoxic activity against HepG2 human cancer cell lines with IC₅₀ ranging from 2.27 to 10.71 μM. In addition, selected compounds were tested on histone deacetylase isoforms (HDAC1–11). Molecular docking simulation was also carried out for HDLP enzyme to investigate their HDAC binding affinity. In addition, generation of 3D-pharmacophore model and quantitative structure activity relationship (QSAR) models were combined to explore the structural requirements controlling the observed cytotoxic properties.     

Design,synthesis, and biological evaluation of pyrazole derivatives containing acetamide bond as potential BRAFV600E inhibitors

With the increasingly acquired resistance, relapse and side effects of known marketed BRAF^V600E inhibitors, it’s significant to design the more effective and novel drugs. In this study, a series of novel pyrazole derivatives containing acetamide bond had been designed and synthesized on the basis of analysis of the endogenous ligands extracted from the known B-Raf co-crystals in the PDB database. Then, the compounds were evaluated for biological activities as potential BRAF^V600E inhibitors. The bioassay results in vitro against three human tumor cell lines revealed that some of the compounds showed very impressed antiproliferative property. Among them, the compound 5r with IC₅₀ values of 0.10?±?0.01?μM against BRAF^V600E and 0.96?±?0.10?μM against A375 cell line, showed the most potent inhibitory effect, compared with the positive-controlled agents vemurafenib (IC₅₀?=?0.04?±?0.004?μM for BRAF^V600E, IC₅₀?=?1.05?±?0.10?μM against A375). Further investigation confirmed that the compound 5r could induce A375 cell apoptosis, induce A375 cell death through changing mitochondrial membrane potential, and result in A375 cell arrest at the G1 phase of the cell cycle. Docking simulations results indicated that the compound 5r could bind tightly at the BRAF^V600E active site. Meanwhile, 3D-QSAR model suggested that these compounds may be potential anticancer inhibitors. Overall, the article provided some new molecular scaffolds for the further BRAF^V600E inhibitors.     

The redox potentials of the b-type cytochromes of higher plant chloroplasts

1. In fresh chloroplasts, three b-type cytochromes exist. These are b-559_HP (λ_max, 559 nm; E_m at pH 7, +370 mV; pH-independent E_m), b-559_LP (λ_max, 559 nm; E_m at pH 7, +20 mV; pH-independent E_m) and b-563 (λ_max, 563 nm; E_m at pH 7, ?110 mV; pH-independent E_m). b-559_HP may be converted to a lower potential form (λ_max, 559 nm; E_m at pH 7, +110 mV; pH-independent E_m).2. In catalytically active b-f particle preparations, three cytochromes exist. These are cytochrome f (λ_max, 554 nm; E_m at pH 7, +375 mV, pK on oxidised cytochrome at pH 9), b-563 (λ_max, 563 nm; E_m at pH 7, ?90 mV, small pH-dependence of E_m) and a b-559 species (λ_max, 559 nm, E_m at pH 7, +85 mV; pH-independent E_m).3. A positive method of demonstration and estimation of b-559_LP in fresh chloroplasts is described which involves the use of menadiol as a selective reductant of b-559_LP.     

Discovery of novel spiro[chromane-2,4′-piperidine] derivatives as potent and orally bioavailable G-protein-coupled receptor 119 agonists

Herein, we describe the discovery, synthesis, and evaluation of a novel series of spiro[chromane-2,4′-piperidine] derivatives as G-protein-coupled receptor 119 agonists. Their initial design exploited the conformational restriction in the linker-to-tail moiety, which was a key concept in this study, to give lead compound 11 (EC₅₀?=?369?nM, E_max?=?82%). An extensive structure–activity relationship study resulted in the identification of the optimized drug candidate (R)-29 (EC₅₀?=?54?nM, E_max?=?181%). The defining structural features of the series were a terminal benzyl-type bulky substituent and a methylene linker between the sulfonyl and phenyl groups, both of which were in the head moiety as well as the spiro-type scaffold in the linker-to-tail moiety. An in vivo oral glucose-tolerance test using C57BL/6N mice showed that (R)-29 reduced glucose excursion at a dose of 3?mg/kg in a dose-dependent manner.     

Effect of oxidation-reduction potential on light-induced cytochrome and bacteriochlorophyll reactions in chromatophores from the photosynthetic green bacterium Chlorobium

The reaction center bacteriochlorophyll of Chlorobium thiosulfatophilum has a midpoint oxidation-reduction potential (E_m) of +330 mV. Its photooxidation is unaffected by oxidation-reduction potentials in the range from +260 mV to ?70 mV but on further reduction is attenuated to zero in a one-electron transition with an E_m of ?130 mV.A c-type cytochrome with an E_m of +220 mV and absorption maxima at 551–552 nm (α-band) and 420 nm (γ-band) is present in Chlorobium chromatophores and undergoes photooxidation. Cytocrome c photooxidation is attenuated to zero in two 1-electron steps with E_m of +30 mV and ?130 mVPossible roles for +30 mV and ?130 mV components in photosynthetic electron transport in Chlorobium are discussed.     

Design,synthesis and biological evaluation of lazabemide derivatives as inhibitors of monoamine oxidase

In the studied a series novel of lazabemide derivatives were designed, synthesized and evaluated as inhibitors of monoamine oxidase (MAO-A or MAO-B). These compounds used lazabemide as the lead compound, and the chemistry structures were modified by used the bioisostere and modification of compound with alkyl principle. The two types of inhibitors (inhibition of MAO-A and inhibition of MAO-B) were screened by inhibition activity of MAO. In vitro experiments showed that compounds 3a, 3d and 3f had intensity inhibition the biological activity of MAO-A, while compounds 3i and 3m had intensity inhibition the biological activity of MAO-B. It could be seen from the data of inhibition activity experiments in vitro, that the compound 3d was IC₅₀?=?3.12?±?0.05?μmol/mL of MAO-A and compound 3m was IC₅₀?=?5.04?±?0.06?μmol/mL. In vivo inhibition activity experiments were conducted to evaluate the inhibitory activity of compounds 3a, 3d, 3f, 3i and 3m by detecting the contents of 5-HT, NE, DA and activity of MAO-A and MAO-B in plasma and brain tissue. In vivo inhibition activity evaluation results showed that the compounds 3a, 3d, 3f, 3i and 3m had increased the contents of 5-HT, NE and DA in plasma and brain tissues. Meanwhile, the determination results activity of MAO in plasma and brain tissue showed that the compounds 3a, 3d, and 3f had a significant inhibitory effect on the activity of MAO-A, while the compounds 3i and 3m showed inhibitory effect on the activity of MAO-B. This study provided a new inhibitors for inhibiting of MAO activity.     

Synthesis and biological evaluation of a novel 99mTc cyclopentadienyl tricarbonyl complex ([(Cp-R)99mTc(CO)3]) for sigma-2 receptor tumor imaging

We report the design, synthesis and biological evaluation of a novel ^99mTc 4-(4-cyclohexylpiperazine-1-yl)-butan-1-one-1-cyclopentadienyltricarbonyl technetium ([^99mTc]5) as a potential SPECT tracer for imaging of σ₂ receptors in tumors. [^99mTc]5 was prepared in 25 ± 5% isolated radiochemical yield with radiochemical purity of >99% via double-ligand transfer (DLT) reaction from the ferrocene precursor 2b (4-(4-cyclohexylpiperazine-1-yl)-1-ferrocenylbutan-1-one). The corresponding Re-complex 4 and the ferrocenyl complex 2b showed relatively high affinity towards σ₂ receptors in in vitro competition binding assay (K_i values of 4 and 2b were 64.4 ± 18.5 nM and 43.6 ± 21.3 nM, respectively) and moderate to high selectivity versus σ₁ receptors (K_iσ₁/K_iσ₂ ratios were 12.5 and 95.5, respectively). The log D value of [^99mTc]5 was determined to be 2.52 ± 0.33. Biodistribution studies in mice revealed comparably high initial brain uptake of [^99mTc]5 and slow washout. Administration of haloperidol 5 min prior to injection of [^99mTc]5 significantly reduced the radiotracer uptake in brain, heart, lung, and spleen by 40–50% at 2 h p.i.. Moreover, [^99mTc]5 showed high uptake in C6 glioma cell lines (8.6%) after incubation for 1 h. Blocking with haloperidol to compete with [^99mTc]5 significantly reduced the cell uptake. Preliminary blocking study in C6-brain-tumor bearing rats showed that [^99mTc]5 binds to σ receptors in the brain-tumor specifically. These results are encouraging for further exploration of ^99mTc-labeled probes for σ₂ receptor tumor imaging in vivo.     

Updating maintenance energy requirement for the current sheep flocks and the associated effect of nutritional and animal factors

There is evidence indicating that using the current UK energy feeding system to ration the present sheep flocks may underestimate their nutrient requirements. The objective of the present study was to address this issue by developing updated maintenance energy requirements for the current sheep flocks and evaluating if these requirements were influenced by a range of dietary and animal factors. Data (n = 131) used were collated from five experiments with sheep (5 to 18 months old and 29.0 to 69.8 kg BW) undertaken at the Agri-Food and Biosciences Institute of the UK from 2013 to 2017. The trials were designed to evaluate the effects of dietary type, genotype, physiological stage and sex on nutrient utilization and energetic efficiencies. Energy intake and output data were measured in individual calorimeter chambers. Energy balance (E_g) was calculated as the difference between gross energy intake and a sum of fecal energy, urine energy, methane energy and heat production. Data were analysed using the restricted maximum likelihood analysis to develop the linear relationship between E_g or heat production and metabolizable energy (ME) intake, with the effects of a range of dietary and animal factors removed. The net energy (NE_m) and ME (ME_m) requirements for maintenance derived from the linear relationship between E_g and ME intake were 0.358 and 0.486 MJ/kg BW^0.75, respectively, which are 40% to 53% higher than those recommended in energy feeding systems currently used to ration sheep in the USA and the UK. Further analysis of the current dataset revealed that concentrate supplement, sire type or physiological stage had no significant effect on the derived NE_m values. However, female lambs had a significantly higher NE_m (0.352 v. 0.306 or 0.288 MJ/kg BW^0.75) or ME_m (0.507 v. 0.441 or 0.415 MJ/kg BW^0.75) than those for male or castrated lambs. The present results indicate that using present energy feeding systems in the UK developed over 40 years ago to ration the current sheep flocks could underestimate maintenance energy requirements. There is an urgent need to update these systems to reflect the higher metabolic rates of the current sheep flocks.     

Effect of phospholipid on the redox potential and enzymic properties of cytochromes b.

The effects of phospholipid on the redox behavior of b cytochromes in succinate-cytochrome c reductase, the cytochrome b-c₁ complex, and an isolated cytochrome b preparation were investigated by the oxidative and reductive titrations. Three E_m values of cytochrome b were observed in the phospholipid-sufftcient and -depleted succinate-cytochrome c reductase. Their midpoint potentials at pH 7.4 are 75, 75, and ?100 mV for the sufficient and 10, ?30, and ?160 mV for the depleted reductase. The molar distribution of the b cytochromes of these E_m values correspond to 30, 30, and 40%, respectively. The E_m values of the isolated cytochrome b preparations were not affected by addition of phospholipids. The isolated b preparation contained two components of equal concentration with E_m values of ?85 and ?200 mV. No direct correlation between enzymic activity and the amount of high potential b cytochromes present in the systems was demonstrated. Very little difference was observed in redox behavior of b cytochromes between the aged inactive preparations of phospholipid-depleted reductase and that of freshly prepared reconstitutively active enzyme.     

A relationship between the midpoint potential of the primary acceptor and low temperature photochemistry in photosystem II

Redox titrations of the photo-induced pheophytin EPR signal in Photosystem II show two transitions which reflect the redox state of Q. The high potential wave (E_m ? ?50 mV) can be photo-induced at 5 K and 77 K. The low potential wave (E_m ? ?275 mV) required illumination at 200 K. This indicates the presence of two kinds of PS-II reaction centres differing in terms of the competence of their donors at low temperature and the E_m-values of their acceptors. Measurements of the semiquinone-iron acceptor also demonstrate functional heterogeneity at low temperature. This is the first observation of the semiquinone-iron acceptor in a non-mutant species.     

Structural features of group V A xanthates. The crystal and molecular structures of tris(O-isopropylxanthatoarsenic(III), antimony(III) and -bismuth(II)

The crystal structures of the title compounds, M(S₂COⁱC₃H₇)₃, M = As(III), (1); Sb(III), (2); and Bi(III), (3) have been determined by three dimensional X-ray diffraction techniques and refined by a least square method. Crystals of (1) and (2) are isomorphous and both crystallize in the rhombohedral space group R$\text{3}$, with unit cell parameters for (1) a_hex = 11.559(2), c_hex = 28.131(3) Å and for (2) a_hex = 11.696(2) and c_hex = 28.135(2) Å, Z = 6. The central metal atom in both (1) and (2) is coordinated by three asymmetrically chelating xanthate ligands [AsS 2.305(2) and 2.978(2) Å and SbS 2.508(1) and 3.006(1) Å] which form a distorted octahedral environment consistent with the presence of a stereochemically active lone pair of electrons. Crystals of (3) are orthorhombic, space group Pnma, Z = 4 with dimensions a = 11.003(3), b = 20.833(4) and c = 9.428(2) Å. The environment of the bismuth atom in (3) is seven coordinate and is comprised of six sulphur atoms, derived from three asymmetrically coordinating xanthate ligands, and a bridging sulphur atom from a neighbouring molecule which results in the formation a polymeric array. For (1) final R and R_W 0.050 and 0.047 respectively for 936 reflections [I ? 3σ(I); (2) R 0.040, R_w 0.040 for 1455 reflections I ? 2σ(I)]; and (3) R 0.052, R_w 0.039 for 1796 reflections [I ? 2σ(I).