Resolution of end-to-end diffusion coefficients and distance distributions of flexible molecules using fluorescent donor-acceptor and donor-quencher pairs.

We used time-dependent fluorescence energy transfer, time-dependent collisional quenching, and global analysis of the data resulting from these through-space and contact interactions to recover the end-to-end distance distributions and diffusion coefficients of flexible fluorescent molecules. The fluorescence decays of covalently linked tryptamine-acceptor and tryptamine-quencher pairs were measured by the frequency-domain method. These data were fit using numerical solutions of the differential equation, which predicts the time- and distance-dependent population of the excited state donors in the presence of energy transfer or collisional quenching, followed by transformation to the frequency domain for nonlinear least-squares comparison with the experimental data. We found that the energy transfer data for the donor-acceptor pair alone were adequate to recover the starting distribution and the end-to-end diffusion coefficient; however, the resolution is dramatically improved by the use of both the through-space and contact interactions.     

Preface Dietary phytochemicals and human health

Phytochemistry Reviews -     

Isolation and characterization of carboxypeptidase Ⅲ from germinating triticale grains

Carboxypeptidase Ⅲ from germinating triticale grains was purified 434.2-fold with a six-step procedure including： homogenization, ammonium sulfate precipitation, cation-exchange chromatography on CM-cellulose, gel filtration chromatography on Sephadex G-150, cation-exchange chromatography on SP8HR column （HPLC）, and affinity chromatography on CABSSepharose 4B. Triticale carboxypeptidase Ⅲ is a monomer with a molecular weight of 45 kDa, which optimally hydrolyzes peptides at temperature 30-50℃ and pH 4.6. N-CBZ-Ala-Phe, N-CBZ-Ala-Leu, and N-CBZ-AIa-Met are hydrolyzed at the highest rates. Amino acids with aromatic or large aliphatic side chains are preferred in position P1＇, whereas the presence of these types of groups in position P1 of the substrate results in a lower rate of hydrolysis. Peptides containing glutamic acid in positions P1 are poor substrates for the enzyme. This phenomenon suggests the hydrophobic substrate-binding sites S1 and S1＇. The active site contains serine since diisopropylfluorophosphate and phenylmethanesulfonyl fluoride reduce the activity by 89.9% and 81.5%, respectively. Moreover, the activity of triticale carboxypeptidase Ⅲ is reduced by mercury ions and organomercurial compounds, which suggests the presence of a sulfhydryl group adjacent to the active site of the enzyme. Identification of purified enzyme by mass spectrometry method demonstrated that the enzyme is a homolog of barley carboxypeptidaseⅢ.     

Xanthophyll-induced aggregation of LHCII as a switch between light-harvesting and energy dissipation systems

The xanthophyll cycle pigments, violaxanthin and zeaxanthin, present outside the light-harvesting pigment-protein complexes of Photosystem II (LHCII) considerably enhance specific aggregation of proteins as revealed by analysis of the 77 K chlorophyll a fluorescence emission spectra. Analysis of the infrared absorption spectra in the Amide I region shows that the aggregation is associated with formation of intermolecular hydrogen bonding between the α helices of neighboring complexes. The aggregation gives rise to new electronic energy levels, in the Soret region (530 nm) and corresponding to the Q spectral region (691 nm), as revealed by analysis of the resonance light scattering spectra. New electronic energy levels are interpreted in terms of exciton coupling of protein-bound photosynthetic pigments. The energy of the Q excitonic level of chlorophyll is not high enough to drive the light reactions of Photosystem II but better suited to transfer excitation energy to Photosystem I, which creates favourable energetic conditions for the state I-state II transition. The lack of fluorescence emission from this energy level, at physiological temperatures, is indicative of either very high thermal energy conversion rate or efficient excitation quenching by carotenoids. Chlorophyll a fluorescence was quenched up to 61% and 34% in the zeaxanthin- and violaxanthin-containing samples, respectively, as compared to pure LHCII. Enhanced aggregation of LHCII, observed in the presence of the xanthophyll cycle pigments, is discussed in terms of the switch between light-harvesting and energy dissipation systems.     

Toxorhina (Ceratocheilus) caucasiensis,a new species from the Middle Miocene of Stavropol (northern Caucasus,USSR) (Diptera,Limoniidae)

Middle Miocene limnic deposits from Stavropol contain wings of the limomidToxorhina (Ceratocheilus) caucasiensis n. sp. Recent species of this genus are distributed in tropic regions around the world.     

Possible humoral mechanism of 2450-MHz microwave-induced increase in complement receptor positive cells

These studies indicate that the increase in the frequency of complement receptor-positive (CR⁺) spleen cells observed 6 days after a 30-min exposure to 2450-MHz microwaves is not the result of microwave-induced alterations of lymphocyte recirculation patterns, but is mediated by a soluble, humoral factor produced by cells within the spleen.     

Competing Models of Stability in Complex, Evolving Systems: Kauffman vs. Simon

I criticize Herbert Simon's argument for the claim that complex natural systems must constitute decomposable, mereological or functional hierarchies. The argument depends on certain assumptions about the requirements for the successful evolution of complex systems, most importantly, the existence of stable, intermediate stages in evolution. Simon offers an abstract model of any process that succeeds in meeting these requirements. This model necessarily involves construction through a decomposable hierarchy, and thus suggests that any complex, natural, i.e., evolved, system is constituted by a decomposable hierarchy. I argue that Stuart Kauffman's recent models of genetic regulatory networks succeed in specifying processes that could meet Simon's requirements for evolvability without requiring construction through a decomposable hierarchy. Since Kauffman's models are at least as plausible as Simon's model, Simon's argument that complex natural systems must constitute decomposable, mereological or functional hierarchies does not succeed.     

An exploration of the effects of L- and D-tetrahydroisoquinoline-3-carboxylic acid substitutions at positions 2,3 and 7 in cyclic and linear antagonists of vasopressin and oxytocin and at position 3 in arginine vasopressin

We have investigated the effects of mono-substitutions with the conformationally restricted amino acid, 1,2,3,4 tetrahydroisoquinoline-3-carboxylic acid (Tic) at position 3 in arginine vasopressin (AVP), at positions 2, 3 and 7 in potent non-selective cyclic AVP V₂/V_1a antagonists, in potent and selective cyclic and linear AVP V_1a antagonists, in a potent and selective oxytocin antagonist and in a new potent linear oxytocin antagonist Phaa-D -Tyr(Me)-Ile-Val-Asn-Orn-Pro-Orn-NH₂ (10). We report here the solid-phase synthesis of peptide 10 together with the following Tic-substituted peptides: 1, [Tic³]AVP; 2, d(CH₂)₅[D -Tic²]VAVP; 3, d(CH₂)₅[D -Tyr(Et)²Tic³]VAVP; 4, d(CH₂)₅[Tic²Ala-NH₂⁹]AVP; 5, d(CH₂)₅[Tyr(Me)², Tic³, Ala-NH₂⁹]AVP; 6, d(CH₂)₅ [Tyr(Me)², Tic⁷]AVP; 7, Phaa-D -Tyr(Me)-Phe-Gln-Asn-Lys-Tic-Arg-NH₂; 8, desGly-NH₂,d(CH₂)₅[Tic²,Thr⁴]OVT; 9, desGly-NH₂d(CH₂)₅[Tyr(Me)²Thr⁴, Tic⁷]OVT; 11, Phaa-D-Tic-Ile-Val-Asn-Orn-Pro-Orn-NH₂, using previously described methods. The protected precursors were synthesized by the solid-phase method, cleaved, purified and deblocked with sodium in liquid ammonia to give the free peptides 1–11 which were purified by methods previously described. Peptides 1–11 were examined for agonistic and antagonistic potency in oxytocic (in vitro, without Mg²⁺) and AVP antidiuretic (V₂-receptor) and vasopressor (V_1a-receptor) assays. Tic³ substitution in AVP led to drastic losses of V₂, V_1a and oxytocic agonistc activities in peptide 1.L - and D -Tic² substitutions led to drastic losses of anti-V₂/anti-V_1a and anti-oxytocic potencies in peptides 2, 4, 8 and 11 (peptide 2 retained substantial anti-oxytocic potency; pA₂ = 7.25 ± 0.25). Whereas Tic³ substitution in the selective V_1a antagonist d(CH₂)₅[Tyr(Me)², Ala-NH₂⁹]APV(C) led to a drastic reduction in anti-V_1a potency (from anti-V_1a pA₂) 8.75 to 6.37 for peptide 5, remarkably, Tic³ substitution in the V₂/V_1a antagonist d(CH₂)₅[D -Tyr(Et)²]VAVP(B) led to full retention of anti-V₂ potency and a 95% reduction in anti-V_1a potency. With an anti-V₂ pA₂ = 7.69 ± 0.05 and anti-V_1a pA₂ = 6.95 ± 0.03, d(CH₂)₅[D -Tyr(Et)²,Tic³]VAVP exhibits a 13-fold gain in anti-V₂/anti-V_1a selectivity compared to (B). Tic⁷ substitutions are very well tolerated in peptides 6, 7 and 9 with excellent retention of the characteristic potencies of the parent peptides. The findings on the effects of Tic³ substitutions reported here may provide promising leads to the design of more selective and possibly orally active V₂ antagonists for use as pharmacological tools and as therapeutic clinical agents for the treatment of the syndrome of the inappropriate secretion of antidiuretic hormone (SIADH).     

Allelopathic potential of glucosinolates (mustard oil glycosides) and their degradation products against wheat

A number of glucosinolates and isothiocyanates were tested for their allelopathic potential against wheat. Most of the glucosinolates showed no activity against wheat, with the exception of glucobrassicin which was moderately active, as was sinapine thiocyanate. Isothiocyanates showed high activity against wheat germination and seedling growth. The most active compound, 2-phenethyl ITC completely inhibited wheat germination at 500 ppm. Allyl ITC showed high activity whereas other isothiocyanates tested were only moderately active. The data is discussed in relation to the possible use of some mustard species for effective weed control.