The abortifacient effect of 16,16-dimethyl-trans-δ2-PGE1 methyl ester,a new prostaglandin analogue,on mid-trimester pregnancies and long-term follow-up observations

The present clinical trials revealed that 16,16-Dimethyl-trans-δ²-PGE₁ methyl ester in the form of vaginal suppositories is highly effective in inducing mid-trimester termination of pregnancies. It also showed that prior treatment with laminaria and metreurynter may enhance the success rate while reducing the incidence and severity of side effects. It is easy and safe to use clinically, with minimal side effects, and in our series, revealed no deleterious effects on ensuing reproductive physiology. However, the definite mechanism involved in the action of this new analogue to cause myometrial contractions is still not completely understood, and requires further intensive investigation.     

Studies on the conformation of amino acids. X. Conformations of norvalyl, leucyl and aromatic side groups in a dipeptide unit

Backbone-side group conformations of amino acid residues including one or two δ-carbons in the side group have been investigated. Conformational energies of norvalyl, leucyl, phenylalanyl, tyrosyl, tryptophenyl, and histidinyl side groups in a dipeptide unit have been calculated by using classical energy expressions. The side group conformations about the C^α—C^β and C^β—C^γ bonds are restricted to specific values of the respective rotational angles. Thus, most favourable positions of γ- and δ-atoms of a linear side-chain (norvalyl) are restricted to (γ_I, δ_II) (γ_II, δ_I), (γ_II, δ_II), (γ_III, δ_II), and (γ_III, δ_III), whereas those of the side-chain branching at a sp³ γ-atom (leueyl) are further restricted. It is also shown that there is a definite correlation between the orientations of the two peptide planes and that of the planar group of the aromatic side chain of phenylalanyl type residues. The studies bring out an important fact that while the γ-atoms have definite and characteristic effects on the backbone rotational angles ? and ψ, the δ atoms and beyond have no effects on the preferred ? and ψ values. Thus, the preferred backbone conformations are independent of the preferred side group conformations beyond the γ-atom and vice versa. The observed ?, ψ, χ¹, and χ² values of amino acids, simple peptides, and of the three protein molecules lysozyme, myoglobin, and chymotrypsin have been compared with the theoretical predictions, and the agreement is found to be excellent.     

Design,Synthesis, and Biological Evaluation of Dexibuprofen Derivatives as Novel Anti-Inflammatory,Antioxidant and Molecular Docking Studies

Prodrugs of dexibuprofen having ester moieties instead of free carboxylic acid which involves in gastrointestinal side effects have been synthesized. Dexibuprofen acid was condensed with different alcohols/phenols to afford the ester prodrugs. All of the synthesized prodrugs were characterized by their physical attributes, elemental analysis, FT-IR, ¹H-NMR, and ¹³C-NMR spectroscopy. The in vitro anti-inflammatory studies was done by chemiluminescence technique reflect prodrugs have been more potent, owing to the different chemical structures. Lipoxygenase enzyme inhibition assay was also assess and found compound DR7 with IC₅₀=19.8 μM), DR9 (IC₅₀=24.8 μM) and DR3 (IC₅₀=47.2 μM) as compared with Dexibuprofen (IC₅₀=156.6 μM). It was also evaluated for docking studies revealed that DR7 has found to be more potent anti-inflammatory against 5-LOX (3 V99) as well as analgesic against COX-II (5KIR) enzyme. Anti-oxidant activities were also performed, DR3 (86.9 %), DR5 (83.5 %), DR7 (93.9 %) and DR9 (87.4 %) were found to be more anti-oxidant as compared to (2S)-2-[4-(2-methylpropyl)phenyl]propanoic acid (52.7 %).     

Effects of isoleucine 135 side chain length on the cofactor donor-acceptor distance within F420H2:NADP+ oxidoreductase: A kinetic analysis

F₄₂₀H₂:NADP⁺ Oxidoreductase (Fno) catalyzes the reversible reduction of NADP⁺ to NADPH by transferring a hydride from the reduced F₄₂₀ cofactor. Here, we have employed binding studies, steady-state and pre steady-state kinetic methods upon wtFno and isoleucine 135 (I135) Fno variants in order to study the effects of side chain length on the donor-acceptor distance between NADP⁺ and the F₄₂₀ precursor, FO. The conserved I135 residue of Fno was converted to a valine, alanine and glycine, thereby shortening the side chain length. The steady-state kinetic analysis of wtFno and the variants showed classic Michaelis-Menten kinetics with varying FO concentrations. The data revealed a decreased k_cat as side chain length decreased, with varying FO concentrations. The steady-state plots revealed non-Michaelis-Menten kinetic behavior when NADPH was varied. The double reciprocal plot of the varying NADPH concentrations displays a downward concave shape, while the NADPH binding curves gave Hill coefficients of less than 1. These data suggest that negative cooperativity occurs between the two identical monomers. The pre steady-state Abs₄₂₀ versus time trace revealed biphasic kinetics, with a fast phase (hydride transfer) and a slow phase. The fast phase displayed an increased rate constant as side chain length decreased. The rate constant for the second phase, remained ~2 s^?1 for each variant. Our data suggest that I135 plays a key role in sustaining the donor-acceptor distance between the two cofactors, thereby regulating the rate at which the hydride is transferred from FOH₂ to NADP⁺. Therefore, Fno is a dynamic enzyme that regulates NADPH production.     

Action of tenuazonic acid,a natural phytotoxin,on photosystem II of spinach

Tenuazonic acid (TeA) is a putative phytotoxin obtained from Alternaria alternata, the organism that can cause brown leaf spot disease of Crofton weed (Eupatorium adenophorum). It is demonstrated here that the tenuazonic acid inhibits the activity of photosystem II (PSII); the I₅₀-value is 48 μg mL^?1. Evidences from chlorophyll fluorescence show that tenuazonic acid interrupts electron transport between Q_A and Q_B on the acceptor side of PSII. It does not have an effect on the antenna pigments, the oxygen-evolving complex (OEC) at the donor side of PSII. On the basis of the fluorescence induction kinetics and competition experiments with [¹⁴C]atrazine, it is shown that tenuazonic acid does not share the same binding environment with atrazine despite their common action target: the Q_B-site. It is concluded that tenuazonic acid is a member of a novel class of PSII inhibitors.     

Cadmium exerts its toxic effects on photosynthesis via a cascade mechanism in the cyanobacterium,Synechocystis PCC 6803

Despite intense research, the mechanism of Cd²⁺ toxicity on photosynthesis is still elusive because of the multiplicity of the inhibitory effects and different barriers in plants. The quick Cd²⁺ uptake in Synechocystis PCC 6803 permits the direct interaction of cadmium with the photosynthetic machinery and allows the distinction between primary and secondary effects. We show that the CO₂‐dependent electron transport is rapidly inhibited upon exposing the cells to 40 µm Cd²⁺ (50% inhibition in ～15 min). However, during this time we observe only symptoms of photosystem I acceptor side limitation and a build of an excitation pressure on the reaction centres, as indicated by light‐induced P700 redox transients, O₂ polarography and changes in chlorophyll a fluorescence parameters. Inhibitory effects on photosystem II electron transport and the degradation of the reaction centre protein D1 can only be observed after several hours, and only in the light, as revealed by chlorophyll a fluorescence transients, thermoluminescence and immunoblotting. Despite the marked differences in the manifestations of these short‐ and long‐term effects, they exhibit virtually the same Cd²⁺ concentration dependence. These data strongly suggest a cascade mechanism of the toxic effect, with a primary effect in the dark reactions.     

The side chain of ubiquinone plays a critical role in Na+ translocation by the NADH-ubiquinone oxidoreductase (Na+-NQR) from Vibrio cholerae

The Na⁺-pumping NADH-ubiquinone (UQ) oxidoreductase (Na⁺-NQR) is an essential bacterial respiratory enzyme that generates a Na⁺ gradient across the cell membrane. However, the mechanism that couples the redox reactions to Na⁺ translocation remains unknown. To address this, we examined the relation between reduction of UQ and Na⁺ translocation using a series of synthetic UQs with Vibrio cholerae Na⁺-NQR reconstituted into liposomes. UQ₀ that has no side chain and UQ_CH3 and UQ_C2H5, which have methyl and ethyl side chains, respectively, were catalytically reduced by Na⁺-NQR, but their reduction generated no membrane potential, indicating that the overall electron transfer and Na⁺ translocation are not coupled. While these UQs were partly reduced by electron leak from the cofactor(s) located upstream of riboflavin, this complete loss of Na⁺ translocation cannot be explained by the electron leak. Lengthening the UQ side chain to n-propyl (C₃H₇) or longer significantly restored Na⁺ translocation. It has been considered that Na⁺ translocation is completed when riboflavin, a terminal redox cofactor residing within the membrane, is reduced. In this view, the role of UQ is simply to accept electrons from the reduced riboflavin to regenerate the stable neutral riboflavin radical and reset the catalytic cycle. However, the present study revealed that the final UQ reduction via reduced riboflavin makes an important contribution to Na⁺ translocation through a critical role of its side chain. Based on the results, we discuss the critical role of the UQ side chain in Na⁺ translocation.     

Identical Ring Cleavage Products during Anaerobic Degradation of Naphthalene, 2-Methylnaphthalene, and Tetralin Indicate a New Metabolic Pathway

Anaerobic degradation of naphthalene, 2-methylnaphthalene, and tetralin (1,2,3,4-tetrahydronaphthalene) was investigated with a sulfate-reducing enrichment culture obtained from a contaminated aquifer. Degradation studies with tetralin revealed 5,6,7,8-tetrahydro-2-naphthoic acid as a major metabolite indicating activation by addition of a C₁ unit to tetralin, comparable to the formation of 2-naphthoic acid in anaerobic naphthalene degradation. The activation reaction was specific for the aromatic ring of tetralin; 1,2,3,4-tetrahydro-2-naphthoic acid was not detected. The reduced 2-naphthoic acid derivatives tetrahydro-, octahydro-, and decahydro-2-naphthoic acid were identified consistently in supernatants of cultures grown with either naphthalene, 2-methylnaphthalene, or tetralin. In addition, two common ring cleavage products were identified. Gas chromatography-mass spectrometry (GC-MS) and high-resolution GC-MS analyses revealed a compound with a cyclohexane ring and two carboxylic acid side chains as one of the first ring cleavage products. The elemental composition was C₁₁H₁₆O₄ (C₁₁H₁₆O₄-diacid), indicating that all carbon atoms of the precursor 2-naphthoic acid structure were preserved in this ring cleavage product. According to the mass spectrum, the side chains could be either an acetic acid and a propenic acid, or a carboxy group and a butenic acid side chain. A further ring cleavage product was identified as 2-carboxycyclohexylacetic acid and was assumed to be formed by β-oxidation of one of the side chains of the C₁₁H₁₆O₄-diacid. Stable isotope-labeling growth experiments with either ¹³C-labeled naphthalene, per-deuterated naphthalene-d₈, or a ¹³C-bicarbonate-buffered medium showed that the ring cleavage products derived from the introduced carbon source naphthalene. The series of identified metabolites suggests that anaerobic degradation of naphthalenes proceeds via reduction of the aromatic ring system of 2-naphthoic acid to initiate ring cleavage in analogy to the benzoyl-coenzyme A pathway for monoaromatic hydrocarbons. Our findings provide strong indications that further degradation goes through saturated compounds with a cyclohexane ring structure and not through monoaromatic compounds. A metabolic pathway for anaerobic degradation of bicyclic aromatic hydrocarbons with 2-naphthoic acid as the central intermediate is proposed.     

Synthesis of New Ester Derivatives of Salicylic Acid and Evaluation of Their COX Inhibitory Potential

Salicylic acid is an NSAID with serious side effects on the GIS. The side effects of salicylic acid on the GIS are slightly reduced by acetylating salicylic acid. 12 new ester analogs of salicylic acid were synthesized with high yields in this study. The chemical structures of the synthesized compounds were characterized by ¹H-NMR, ¹³C-NMR, and HRMS spectra. The inhibitory potential of the compounds was evaluated on COXs by in vitro and in silico studies. The COX2 inhibitory activity of the most potent inhibitor MEST1 (IC₅₀: 0.048 μM) was found to be much higher than the COX2 inhibitory activity of aspirin (IC₅₀: 2.60 μM). In docking studies, the strongest inhibitor among the compounds synthesized was predicted to be MEST1, with the lowest binding energy. Docking studies revealed that MEST1 extends from the hydrophobic channel to the top of the cyclooxygenase active site, forming various interactions with residues in the binding pocket.     

Biomimetic Synthesis of Collagen/Nano-Hydroxyapitate Scaffold for Tissue Engineering

This paper reports a precipitation method for the fabrication of compositionally graded biomimetic collagen/nano-hydroxyapatite (HA) composite scaffold. The method is centrifugation based and produce the precipitation of nano-HA crystallites in situ (calcium ions (Ca²⁺) react phosphate ions (PO₄³⁻) and precipitate a non-stoichiometric hydroxyapatite). It was observed that prism needle-like nano-HA crystallites (about 2.5 nm × 3 nm× 25 nm) precipitated on collagen fibrils in the interior of collagen matrix. Chemical and microstructure analysis revealed a gradient of the Ca to P ratio across the width of the scaffold, lead to the formation of a HA-rich side and a HA-deplete side of scaffold. The HA-rich side featured low porosity and agglomerates of the nano-HA crystallites; while HA-depleted side featured higher porosity and nano-HA crystallites integrated with collagen fibrils to form a porous network structure.     

Investigating the membrane orientation and transversal distribution of 17β-estradiol in lipid membranes by solid-state NMR

17β-Estradiol (E₂) is a potent estrogen, which modulates many important cellular functions by binding to specific estrogen receptors located in the cell nucleus and also on the plasma membrane. We have studied the membrane interaction of E₂ using a combination of solid-state NMR methods. ²H NMR results indicate that E₂ does not cause a condensation effect of the surrounding phospholipids, which is contrary to the effects of cholesterol, and only very modest E₂ induced alterations of the membrane structure were detected. ¹H magic-angle spinning NMR showed well resolved signals from E₂ as well as of POPC in the membrane-lipid layer. Two-dimensional NOESY spectra revealed intense cross-peaks between E₂ and the membrane lipids indicating that E₂ is stably inserted into the membrane. The determination of intermolecular cross-relaxation rates revealed that E₂ is broadly distributed in the membrane with a maximum of the E₂ distribution function in the upper chain region of the membrane. We conclude that E₂ is highly dynamic in lipid membranes and may undergo rotations as it exhibits two polar hydroxyl groups on either side of the molecule.     

Proton NMR study of the conformation of bradykinin: pH titration.

pH titration by ¹H-NMR spectroscopy of the peptide hormone bradykinin was carried out in ²H₂O. Assignment of all α-proton signals and of most of the other resonances permitted the extraction of vicinal coupling constants ³J_αβ,β′ from which side chain conformation of all residues could be followed and analyzed as a function of pH. It is shown that the ionization of the terminal COOH group affects simultaneously the Arg-9 and Phe-8 chemical shifts and side chain orientation, and the non-equivalence of the Gly-4 methylene protons. Cooperative effects along the peptide backbone or a folded structure of the C-terminal part of bradykinin could explain this effect.     

Mitochondrial aldehyde dehydrogenase 2 accentuates aging-induced cardiac remodeling and contractile dysfunction: role of AMPK,Sirt1, and mitochondrial function

Cardiac aging is associated with compromised myocardial function and morphology although the underlying mechanism remains elusive. Aldehyde dehydrogenase 2 (ALDH2), an essential mitochondrial enzyme governing cardiac function, displays polymorphism in humans. This study was designed to examine the role of ALDH2 in aging-induced myocardial anomalies. Myocardial mechanical and intracellular Ca²⁺ properties were examined in young (4–5 months) and old (26–28 months) wild-type and ALDH2 transgenic mice. Cardiac histology, mitochondrial integrity, O₂⁻ generation, apoptosis, and signaling cascades, including AMPK activation and Sirt1 level were evaluated. Myocardial function and intracellular Ca²⁺ handling were compromised with advanced aging; the effects were accentuated by ALDH2. Hematoxylin and eosin and Masson trichrome staining revealed cardiac hypertrophy and interstitial fibrosis associated with greater left-ventricular mass and wall thickness in aged mice. ALDH2 accentuated aging-induced cardiac hypertrophy but not fibrosis. Aging promoted O₂⁻ release, apoptosis, and mitochondrial injury (mitochondrial membrane potential, levels of UCP-2 and PGC-1α), and the effects were also exacerbated by ALDH2. Aging dampened AMPK phosphorylation and Sirt1, the effects of which were exaggerated by ALDH2. Treatment with the ALDH2 activator Alda-1 accentuated aging-induced O₂⁻ generation and mechanical dysfunction in cardiomyocytes, the effects of which were mitigated by cotreatment with activators of AMPK and Sirt1, AICAR, resveratrol, and SRT1720. Examination of human longevity revealed a positive correlation between life span and ALDH2 gene mutation. Taken together, our data revealed that ALDH2 enzyme may accentuate myocardial remodeling and contractile dysfunction in aging, possibly through AMPK/Sirt1-mediated mitochondrial injury.     

Protective effects of prostaglandins in the isolated gastric mucosa of the eel, Anguilla anguilla

The protective effect of endogenous prostaglandins on the fish gastric mucosa was evaluated by studying the effect of indomethacin and aspirin, known cyclooxigenase inhibitors, on the mucosal ulceration in the isolated gastric sacs of Anguilla anguilla. Gastric sacs devoid of muscle layers were incubated in the presence of indomethacin (10⁻⁴ mol · l⁻¹) or aspirin (10⁻⁴ mol · l⁻¹) in different experimental conditions. Both the anti-inflammatory drugs produced ulcers, but the effects were more severe in the presence of histamine and in the absence of HCO₃ ⁻ in the incubation bath. The effects of prostaglandin E₂ (PGE₂) on acid secretion rate (J_H) and on alkaline secretion rate (J_OH) were evaluated (with the aid of the pH stat method) in isolated gastric mucosa mounted in Ussing chambers. We found that PGE₂ (10⁻⁸–10⁻⁵ mol · l⁻¹) increased J_H in a dose-dependent manner. In tissues pretreated with luminal omeprazole (10⁻⁴ mol · l⁻¹), PGE₂ stimulated gastric alkaline secretion. It was nullified by serosal removal of HCO₃ ⁻ or Na⁺ and by serosal ouabain (10⁻⁴ mol · l⁻¹). These results suggested that prostaglandins also exert their protective effects in fish gastric mucosa. This protection seems partially due to a stimulation of exogenous HCO₃ ⁻ transport from the serosal to the mucosal side. It is likely that this transport is an active transcellular mechanism coupled to Na⁺ transport. Accepted: 14 April 2000     

Quantitative two-dimensional nmr study of dermenkephalin,a highly potent and selective δ-opioid peptide

Dermenkephalin, H-Tyr-(D ) Met-Phe-His-Leu-Met-Asp-NH₂, a highly potent and selective δ-opioid peptide isolated from frog skin, was studied in DMSO-d₆ solution by two-dimensional nmr spectroscopy, including the determination of NH temperature coefficients, the evaluation of ³J coupling constants from phase-sensitive correlated spectroscopy (COSY) and the volumes of nuclear Overhauser effect (NOE) correlations. The two-dimensional NOE spectroscopy (NOESY) spectrum of dermenkephalin revealed sequential, medium-, and long-range effects. To put this information on a quantitative basis, special attention was devoted to J cross-peak suppression, quantification of the NOE volumes and analysis of the overlaps, normalization of the NOEs against diagonal peaks and H_ββ′ geminal interactions. Although most of the dihedral angles deduced from the ³J_Nα coupling constants together with several N_iα_i and α_iN_{i + 1} NOEs pointed to a partially extended peptide backbone, several N_i N_{i + 1} NOEs and β_i N_{i + 1} interactions argued in favor of a folded structure. Moreover, several long-range correlations of strong intensities were found that supported a close spatial proximity between the side chains of D -Met² and Met⁶, Tyr¹ and His⁴, Tyr¹ and Asp⁷, and His⁴ and the C-terminal amide group. In Phe, the g^? rotamer in the side chain is deduced from the ³J_αβ coupling constants and αβ and Nβ NOE correlations. Whereas the amide proton dependency was not indicative of stable hydrogen bonds, the nonuniform values of the temperature coefficient may reflect an equilibrium mixture of folded and extended conformers. The overall data should provide realistic starting models for energy minimization and modelization studies. © 1993 John Wiley & Sons, Inc.     

Search for intermediates of photosynthetic water oxidation

Photosystem II of cyanobacteria and plants incorporates the catalytic centre of water oxidation. Powered and clocked by quanta of light the centre accumulates four oxidising equivalents before oxygen is released. The first three oxidising equivalents are stored on the Mn₄Ca-cluster, raising its formal oxidation state from S₀ to S₃ and the third on Y_Z, producing S₃ Y_Z^ox. From there on water oxidation proceeds in what appears as a single reaction step (S₃ Y_Z^ox(H₂O)₂O₂ + 4H⁺ + S₀. Intermediate oxidation products of bound water had not been detected, until our recent report on the stabilisation of such an intermediate by high oxygen pressure (NATURE 430, 2004, 480–483). Based on the oxygen titration (half-point 2.3 bar) the standard free-energy profile of a reaction sequence with a single intermediate was calculated. It revealed a rather small difference (−3 kJ mol⁻¹) between the starting state [S₃Y_Z^OX and the product state S₀Y_Z + O₂ + 4H⁺ . Here we describe the tests for side effects of exposing core particles to high oxygen pressure. We found the reduction of P₆₈₀^{+ ·} in ns and the reduction/dismutation of quinones at the acceptor side of PSII both unaffected, and the inhibition of the oxygen evolving reaction by exposure to high O₂-pressure was fully reversible by decompression to atmospheric conditions.     

Chymotrypsin inhibitory conformation of dipeptides constructed by side chain–side chain hydrophobic interactions

A complete series of configurationally isomers (L -L , L -D , D -L AND D -D ) of a dipeptide Leu-Phe benzyl ester have been synthesized and assayed for chymotrypsin. In the conformational analysis by 400 MMz ¹H NMR, the L -D and D -L isomers, but not hte L -L and D -D isomers, showed fairly large up field shifts (0.2–0.4 ppm) of Leu-βCH₂ and γCH proton signals, indicating the presence of shielding effects from the benzene ring. In addition to distinct signal splitting of Phe-βCH₂, the NOE enhancement observed between Leu-δCH₃ and Phe-phenyl groups revealed that these groups are in close proximity. These data indicated that L -D and D -L isomers from a hydrophobic core between side chains of adjacent Leu and Phe residues. When the dipeptides were examined for inhibition of chymotrypsin using Ac-Try-OEt as a substrate, the L -L isomer showed no inhibition, itself becoming a substrate. However, the other three isomers inhibited chymotrypsin in a competitive manner, and the D -L isomer was strongest with K_i of 2.2 × 10_?5 M . It was found that the D -L isomer was only slowly hydrolysed but the L (or D )-D isomer was not. H-D -Phe-L -Leu-OBzl with the inverse sequence of H-D -Leu-L -Pre-OBzl inhibited chymotrypsin more strongly (K_i = 6.3 × 10^?6 M ). Since the free acid analogue of the D -L isomer exhibited no inhibition, the benzyl ester moiety itself was thought to be involved in the enzyme inhibition. It is assumed that in the inhibitory conformation the ester-benzyl group fits the S₁ site of chymotrypsin, while the side chain-side chain complexing hydrophobic core fits the S₂ site.     

Is carbonic anhydrase activity of photosystem II required for its maximum electron transport rate?

It is known, that the multi-subunit complex of photosystem II (PSII) and some of its single proteins exhibit carbonic anhydrase activity. Previously, we have shown that PSII depletion of HCO₃^?/CO₂ as well as the suppression of carbonic anhydrase activity of PSII by a known inhibitor of α?carbonic anhydrases, acetazolamide (AZM), was accompanied by a decrease of electron transport rate on the PSII donor side. It was concluded that carbonic anhydrase activity was required for maximum photosynthetic activity of PSII but it was not excluded that AZM may have two independent mechanisms of action on PSII: specific and nonspecific. To investigate directly the specific influence of carbonic anhydrase inhibition on the photosynthetic activity in PSII we used another known inhibitor of α?carbonic anhydrase, trifluoromethanesulfonamide (TFMSA), which molecular structure and physicochemical properties are quite different from those of AZM. In this work, we show for the first time that TFMSA inhibits PSII carbonic anhydrase activity and decreases rates of both the photo-induced changes of chlorophyll fluorescence yield and the photosynthetic oxygen evolution. The inhibitory effect of TFMSA on PSII photosynthetic activity was revealed only in the medium depleted of HCO₃^?/CO₂. Addition of exogenous HCO₃^? or PSII electron donors led to disappearance of the TFMSA inhibitory effect on the electron transport in PSII, indicating that TFMSA inhibition site was located on the PSII donor side. These results show the specificity of TFMSA action on carbonic anhydrase and photosynthetic activities of PSII. In this work, we discuss the necessity of carbonic anhydrase activity for the maximum effectiveness of electron transport on the donor side of PSII.     

1H and 13C nmr studies of cyclic and linear dipeptides containing threonyl,seryl, aspartyl,and histidyl residues

The side-chain conformations of D - orL - Thr, D - or L -Ser, L -Asp, and L - His residues in cyclic and linear dipeptides in D₂O or in DMSO-d₆ are deduced from vicinal (¹H,¹H) and (¹³C, ¹H) coupling constants. Vicinal (¹³C, ¹³C) coupling constants strongly depend on substituents and cannot be used without a more sound analysis. In cyclic dipeptides, the Thr and Ser side chains are folded above the DKP ring, with χ¹ near 60°. The L -Asp side chain interacts more specifically with peptide bonds (χ¹ near 300°). The L - His side chain is more flexible and its conformation depends on the proximity of a second side chain and on solute-solvent interactions. In all cases, this side chain is not completely folded. In linear dipeptides, the conformation of a C-terminal L -His residue is mainly influenced by the end carboxylic group. On the other hand, a N-terminal L -His residue interacts more easily with a neighboring L -Asp residue. In aqueous solution, the imidazole pK_a depends on the proximity of terminal and lateral charged groups but does not reveal any specific interaction in cyclic dipeptides. A comparison between the conformations of cyclic peptides observed in solution, in the crystalline state and calculated by empirical methods, allows one to point out the discriminating role of the packing in crystals, and of solute-solvent interactions in solution.     

Trehalose, Respiration und Photosynthese in dem Farn Ophioglossum, Ein neuer Schattenblattypus

Trehalose, Resipration and Photosynthesis in the Fern Ophioglossum. A new Type of Shade-Leaves.—Trehalose has been identified in the leaf-blades, sporehouses, stems and rhizomes of the fern Ophioglossum vulgatum by paper chromatography. The leaf-blades represent a hitherto undescribed type of shade-leaf. Just like normal shade-leaves, they have a low respiratory activity ～0.2–0.3 mg CO₂ per 50 cm² leaf-blade (one side only) and hour at 20°C and low maximal photosynthesis: 2–2.7 mg CO₂ per 50 cm² leaf-blade (one side only) and hour at 20°C and a CO₂-pressure of 0.25 mm Hg and a light intensity of 20,000 lux. But in contrast to the hitherto described type of shade-leaves, the area per 1 g fresh weight is that of typical sun-leaves which is 35–50 cm² (one side only) per 1 g fresh weight. The large area weight is connected with particularly low dry matter content ～10–11 per cent in the leaf-blades; this indicates that the material is a kind of semisucculent shade-leaf.