Physicochemical properties and antitumor activities for sulfated derivatives of lentinan

Five fractions of lentinan, a β-(1→3)-d-glucan bearing β-(1→6)-d-glucopyranosyl branches, were treated with chlorosulfonic acid for 90 min at 60 °C in pyridine medium to synthesize water-soluble sulfated derivatives having the substitution degree of 1.44–1.76. The ¹³C NMR spectra of the sulfated β-glucans indicated that the C-6 position was preferentially substituted by the sulfate groups. The values of the weight-average molecular weight (M_w), radius of gyration (), and intrinsic viscosity ([η]) of the sulfated lentinan fractions were determined by size-exclusion chromatography with multi-angle laser light scattering (SEC–MALLS) and viscometry in 0.15 M aq NaCl at 25 °C, respectively. The dependence of [η] on M_w for the sulfated lentinan was found to be [η] = 8.93 × 10⁻³ (mL/g) in 0.15 M aq NaCl (for M_w ranging from 14.6 × 10⁴ to 50.4 × 10⁴). On the basis of the Yamakawa–Fujii–Yoshizaki (YFY) theory, the conformational parameters of the sulfated lentinan were calculated as 950 nm⁻¹ for the molar mass per unit contour length (M_L), 4.8 nm for the persistence length (q), and 13.9 for the characteristic ratio (C_∞), indicating relatively extended single flexible chains in solution. The sulfated glucan fractions exhibited in vitro antiproliferative activities against sarcoma 180 (S-180) cells, and their inhibition ratios were lower than that of the triple-helix lentinan, but higher than that for the one with single random-coil lentinan chains.     

6-Ethyl-5-hydroxy-2,7-dimethoxy-1,4-naphthoquinone from Hendersonula toruloidea: A biosynthetic study using C labels detected by nuclear magnetic resonance and C tracers

Production of 6-ethyl-5-hydroxy-2,7-dimethoxy-1,4-naphthoquinone was obtained by growth of Hendersonula toruloidea on Czapek-Dox broth supplemented with malt extract. Stationary cultures were grown at 28°C for 21–22 days yielding about 6 mg of metabolite per 700 ml of culture fluid. The best incorporations of isotopic tracers were obtained by addition at the 20th day of growth, followed by harvest 24–48 hr later. With [2-¹⁴C]acetate, incorporation values were in the range of 0.1–0.3% with dilution values from 2000 to 5900. With [1-¹⁴C]propionate, incorporations were much lower (0.04%) and dilutions much higher (120,000). Activity from [¹⁴CH₃]methionine was incorporated only into the OCH₃ groups (incorporation values, 0.5–0.7%). Nuclear magnetic resonance studies confirmed that propionate was not a precursor. Using [1,2-¹³C]acetate, substantial enrichments were obtained at all carbon atoms except those of the OCH₃ groups. The following pairs of carbon atoms were shown to be derived from acetate units: C-1 + 2, C-3 + 4, C-5 + 10, C-6 + 7, C-8 + 9, C-11 + 12. The biosynthetic pathway is clearly that of acetate plus polymalonate. Experiments with [2-¹³C²H₃]acetate suggested that the “starter” acetate unit was located at positions C-12 + 11.     

Determination of β-glucosidase aggregating factor (BGAF) binding and polymerization regions on the maize β-glucosidase isozyme Glu1

β-Glucosidases (Glu1 and Glu2) in maize specifically interact with a lectin called β-glucosidase aggregating factor (BGAF). We have shown that the N-terminal (Glu⁵⁰–Val¹⁴⁵) and the C-terminal (Phe⁴⁶⁶–Ala⁵¹²) regions of maize Glu1 are involved in binding to BGAF. Sequence comparison between sorghum β-glucosidases (dhurrinases, which do not bind to BGAF) and maize β-glucosidases, and the 3D-structure of Glu1 suggested that the BGAF-binding site on Glu1 is much smaller than predicted previously. To define more precisely the BGAF-binding site, we constructed additional chimeric β-glucosidases. The results showed that a region spanning 11 amino acids (Ile⁷²–Thr⁸²) on Glu1 is essential and sufficient for BGAF binding, whereas the extreme N-terminal region Ser¹–Thr²⁹, together with C-terminal region Phe⁴⁶⁶–Ala⁵¹², affects the size of Glu1–BGAF complexes. The dissociation constants (K_d) of chimeric β-glucosidase–BGAF interactions also demonstrated that the extreme N-terminal and C-terminal regions are important but not essential for binding. To confirm the importance of Ile⁷²–Thr⁸² on Glu1 for BGAF binding, we constructed a chimeric sorghum β-glucosidase, Dhr2 (C-11, Dhr2 whose Val⁷²–Glu⁸² region was replaced with the Ile⁷²–Thr⁸² region of Glu1). C-11 binds to BGAF, indicating that the Ile⁷²–Thr⁸² region is indeed a major interaction site on Glu1 involved in BGAF binding.     

Unidirectional influx and phosphorylation of glucose analogues in cultured astroblasts

Unidirectional influx of¹⁴C-3OMG (3-O-methyl-d-glucose) and rate of phosphorylation of¹⁴C-2DG (2-deoxy-d-glucose) were determined in primary cultures of astroblasts under conditions with neglible unstirred layers. The influx exhibited rate constants between 7.2 and 8.3 min^–1 in the concentration range 2.5–25 mM of unlabeled 3OMG and was considered constant, irrespective of concentration of 3OMG. The rate of phosphorylation of¹⁴C-2DG declined for rising concentrations of 2DG and hence showed saturability. The rate constants ranged from 7.9 to 0.1 min^–1 in the concentration range 0.04–25 mM of 2DG. These results are not consistent with the view that the influx limits the rate of phosphorylation. They support the notion that the influx is not rate limiting for the phosphorylation.     

Sulfated modification and cytotoxicity of <Emphasis Type="Italic">Portulaca oleracea</Emphasis> L. polysaccharides

A water-soluble polysaccharide (POP1) was isolated from Portulaca oleracea L. Four sulfated derivatives of POP1 (POP1-s1, POP1-s2, POP1-s3 and POP1-s4) were prepared by chlorosulfonic acid method with N,N-Dicyclohexylcarbodiimide (DCC) as a dehydration-condensation agent. FT-IR spectra and ¹³C NMR spectra indicated the sulfated groups had been introduced at the C-6 and C-2 positions of POP1. Sulfated derivatives had different degree of substitution (DS) ranging from 1.01 to 1.81, and different weight-average molecular mass (Mw) ranging from 41.4 to 48.5 KDa. Sulfated derivatives except POP1-s5 inhibited the growth of HepG2 cells and Hela cells in vitro significantly, which indicated that sulfated modification could enhance cytotoxicity of POP1 on tumor cells. Flow cytometric studies revealed that sulfated derivatives could mediate the cell-cycle arrest of Hela cells in the S phase.     

Influence of bed media characteristics on ammonia and nitrate removal in shallow horizontal subsurface flow constructed wetlands

Two bed media were tested (gravel and Filtralite) in shallow horizontal subsurface flow (HSSF) constructed wetlands in order to evaluate the removal of ammonia and nitrate for different types of wastewater (acetate-based and domestic wastewater) and different COD/N ratios. The use of Filtralite allowed both higher mass removal rates (1.1 g NH₄–N m⁻² d⁻¹ and 3 g NO₃–N m⁻² d⁻¹) and removal efficiencies (>62% for ammonia, 90–100% for nitrate), in less than 2 weeks, when compared to the ones observed with gravel. The COD/N ratio seems to have no significant influence on nitrate removal and the removal of both ammonia and nitrate seems to have involved not only the conventional pathways of nitrification–denitrification. The nitrogen loading rate of both ammonia (0.8–2.4 g NH₄–N m⁻² d⁻¹) and nitrate (0.6–3.2 g NO₃–N m⁻² d⁻¹) seem to have influenced the respective removal rates.     

Metadynamics modelling of the solvent effect on primary hydroxyl rotamer equilibria in hexopyranosides

Accurate modelling of rotamer equilibria for the primary hydroxyl groups of monosaccharides continues to be a great challenge of computational glycochemistry. The metadynamics technique was applied to study the conformational free energy surfaces of methyl α-d-glucopyranoside and methyl α-d-galactopyranoside, employing the glycam06 force field. For both molecules, seven to eight conformational free-energy minima, differing in the ω (O-5–C-5–C-6–O-6) and χ (C-3–C-4–O-4–HO-4) dihedral angles, were identified in vacuum or in a water environment. The calculated rotamer equilibrium of the primary hydroxyl group is significantly different in vacuum than in water. The major effect of a water environment is the destabilisation of a hydrogen bond between O-4–HO-4 and O-6–HO-6 groups. It was possible to calculate the free-energy differences of individual rotamers with an accuracy of better than 2 kJ/mol. The calculated gg, gt and tg rotamer populations in water are in close agreement with experimental measurements, and therefore support the theoretical background of metadynamics.     

Molecular mass and antitumor activities of sulfated derivatives of α-glucan from Poria cocos mycelia

Two kinds of water-insoluble (1 → 3)-α-d-glucan samples, ab-PCM3-I and ac-PCM3-I, isolated from different Poria cocos mycelia were sulfated, to produce two series of water-soluble derivatives ab-PCM3-I-S1–S5 and ac-PCM3-I-S1–S5, respectively. The derivatives having different weight-average molecular mass (M_w) were produced by changing reaction temperature and time as well as molar ratios between chlorosulfonic acid and number of hydroxyl groups in the glucan. The degrees of substitution (DS) of the sulfated derivatives were analyzed by elemental analysis (EA) to be 0.39–0.67 for ab-PCM3-I-S and 0.73–0.96 for ac-PCM3-I-S, respectively. The M_w and the intrinsic viscosity ([η]) of the samples ab-PCM3-I-S and the ac-PCM3-I-S were measured by size exclusion chromatography combined with laser light scattering (SEC–LLS) and viscometry in phosphate buffer solution (PBS) at 37 °C. The results indicated that their M_w ranged from 2.0 to 11.3 × 10⁴ for the samples ab-PCM3-I-S, and 4.7 to 40.0 × 10⁴ for the samples ac-PCM3-I-S. Moreover, the antitumor activities of the sulfated derivatives ab-PCM3-I-S and ac-PCM3-I-S against Sarcoma 180 tumor cell tested both in vitro and in vivo are significantly higher than those of the native α-d-glucans. Therefore, a moderate range of molecular mass from 2.0 × 10⁴ to 40.0 × 10⁴, relatively high chain stiffness and good water solubility of the sulfated derivatives are beneficial to the enhancement of their antitumor activities.     

Biosynthesis of chondroitin sulfate side chains and hyaluronate time-course studies with cartilage slices of calf ribs under different conditions

The time course of double labeling with ³⁵SO₄²⁻ and [³H]glucosamine was followed in a semi-in vitro system of cartilage slices from calf ribs whose chondroitin sulfate peptide pool consistsof (A) <1% of very short undersulfated side chains of <10 disaccharide units length, (B) 3–5% of short undersulfated longer side chains (16 to 25 disaccharide units), (C) 3–5% of short, slightly oversulfated side chains (16–23 dissacharide units, very probably containing some dermatan sulfate), (D) the bulk material (74–82% of total uronate) of longest, slightly undersulfated or equally sulfated side chains (22–42 disaccharide units).After 10 min incubation rapid chain elongation with [³H]glucosamine and prelabeling with ³⁵SO₄²⁻ of endogenous acceptors are apparent. Chains of type A exhibit highest specific radioactivities. During 30–60 min incubation it is mainly chains of type B that show highest specific radioactivities, after 90 min chains of type C. On the after hand, chains of type D always incorporated the highest total amount of both precursors. Preincubation of slices for 40 min at 37°C strongly enhances labeling rates of all types whilst preincubation for 40 min in an ice-bath enhances mainly ³⁵SO₄²⁻ labeling of types A and B.After 10 min preincubation followed by ³⁵SO₄²⁻ labeling for 60 min a decrease of radioactivity of type A and a distinct increase with type B are observed during the post incubation period. After pulse chase experiment type B exhibit highest specific radioactivities. The data make it evident that under-sulfated short chondroitin sulfate side chains from very rapidly in a well organised manner and grow, by elongation and proceeding sulfation processes, to longer higher sulfated chains.The labeling of the hyaluronate pool is about half of that of the chondroitin sulfate pool after a lag phase of 10 min. The latter increases linearly after 35–45 min incubation time. However, after preincubation and chase experiments the hyaluronate pool is more highly labeled. The data indicate different precursor pools of both biosynthesis mechanisms, probably located in different cell compartments and/or different cartilage cells.     

Electrophysiological evidence for detection and discrimination of pheromonal bile acids by the olfactory epithelium of female sea lampreys (<Emphasis Type="Italic">Petromyzon marinus</Emphasis>)

Electro-olfactograms were used to determine sensitivity and specificity of olfactory organs of female sea lampreys (Petromyzon marinus) to four bile acids: 3-keto petromyzonol sulfate and 3-keto allocholic acid from spermiating males and petromyzonol sulfate and allocholic acid from larvae. Spermiating male bile acids are thought to function as a mating pheromone and larval bile acids as a migratory pheromone. The response threshold was 10^–12 mol l^–1 for 3-keto petromyzonol sulfate and 10^–10 mol l^–1 for the other bile acids. At concentrations above 10^–9 mol l^–1, the sulfated bile acids showed almost identical potency, as did the non-sulfated bile acids. The two sulfated bile acids were more potent than the two non-sulfated ones. In addition, 3-keto petromyzonol sulfate and water conditioned with spermiating males induced similar concentration-response curves and response thresholds. Cross-adaptation experiments demonstrated that the sulfated and non-sulfated bile acids represent different odors to the olfactory epithelium of females. Further exploration revealed that 3-keto petromyzonol sulfate represents a different odor than petromyzonol sulfate, while 3-keto allocholic acid and allocholic acid represent the same odor. Results indicate that male-specific bile acids are potent and specific stimulants to the female olfactory organ, supporting the previous hypothesis that these bile acids function as a pheromone.Abbreviations 3kACA 3-keto allocholic acid - 3kPZS 3-keto petromyzonol sulfate - ACA allocholic acid - ANOVA analysis of variance - ELISA enzyme-linked immunosorbent assay - EOG electro-olfactogram - PIR percent initial response - PZS petromyzonol sulfate - SMW spermiating male washings     

Tryptamine as an endogenous modulator of neuronal sensitivity to serotonin

Research was performed on sensory ganglia isolated from adult rats using intracellular techniques for recording membrane potential and by measuring resistance at the membrane of individual units. It was found that tryptamine at high concentrations manifests serotoninlike activity, but, at concentrations not affecting potential and resistance at the neuronal membrane, either reinforces (at a concentration of 10^–7 M) or attenuates (at 10^–5 M) serotonin (5-HT) effects mediated by type 1A (but not type 2) 5-HT receptors. 5-HT-modulated effects were produced by tryptamine-induced changes in 5-HT sensitivity at the neuronal membrane and remained unchanged by maximum level of this transmitter. Harmane acts similarly to tryptamine, although harmane derivatives (C-412 and C-506 respectively) produce either potentiation or inhibition of 5-HT_1A over the entire concentration range used (of 10^–7 M-10^–5 M). The allosteric nature of 5-HT-modulation by tryptamine and harmane is discussed.M. Gor'kii Medical Institute, Donetsk, Ukrainian SSR. Translated from Neirofiziologiya, Vol. 21, No. 3, pp. 352–357, May–June, 1989.     

Graft copolymerization of N-vinylformamide onto sodium carboxymethylcellulose and study of its swelling, metal ion sorption and flocculation behaviour

The present paper reports the graft copolymerization of N-vinylformamide onto sodium carboxymethylcellulose by free radical polymerization using potassium peroxymonosulphate/thiourea redox system in an inert atmosphere. The reaction conditions for maximum grafting have been optimized by varying the reaction variables, including the concentration of N-vinylformamide (12.0 × 10⁻²–28.0 × 10⁻² mol dm⁻³), potassium peroxymonosulphate (4.0 × 10⁻³–12.0 × 10⁻³ mol dm⁻³), thiourea (1.2 × 10⁻³–4.4 × 10⁻³ mol dm⁻³), sulphuric acid (2.0 × 10⁻³–10.0 × 10⁻³ mol dm⁻³), sodium carboxymethylcellulose (0.2–1.8 g dm⁻³) along with time duration (60–180 min) and temperature (25–45° C). Water swelling capacity, metal ion sorption and flocculation studies of synthesized graft copolymer have been performed with respect to the parent polymer. The graft copolymer has been characterized by FTIR spectroscopy and thermogravimetric analysis.     

Benthic oxygen flux in the highly productive subarctic Lake Myvatn, Iceland: In situ benthic flux chamber study

In situ paired light and dark-stirred benthic flux chambers were used to estimate dissolved oxygen flux across the sediment–water interface in Lake Mývatn, Iceland. Three sampling stations were selected, each station reflecting a specific sedimentary environment, benthic communities, and water depth. During this study the phytoplankton density was low. Spatial and seasonal variations of bottom DO concentration and DO flux have been observed during this study. The oxygen consumption rate at all study sites had a mean of –89 (±44) mmol m^–2 d^–1 while the oxygen production rate due to benthic algae had a mean of 131 (±103) mmol m^–2 d^–1. There was a strong correlation (r=0.91) between oxygen consumption rate and temperature. This was presumably because of the temperature influence on rates of microbial and macrobenthic processes. The mean benthic primary production rate at all study sites was 1216 (±957) mg C m^–2 d^–1 between June 2000 and February 2001. Annual gross benthic primary production was estimated from the gross mean daily benthic DO production (P) and Redfield's C:O₂ ratio of 106:138 to be 420 g C m^–2 y^–1 at station HO, 250 g C m^–2 y^–1 at B2 and 340 g C m^–2 y^–1 at station 95. Thus, the mean gross benthic primary production was estimated as 1151 mg C m^–2 d^–1 at station HO, 685 mg C m^–2 d^–1 at station B2, and 932 mg C m^–2 d^–1 at station 95.     

Structures and stability of N<Subscript>13</Subscript><Superscript>+</Superscript> and N<Subscript>13</Subscript><Superscript>−</Superscript> clusters

The structures and stabilities of eleven N₁₃ ⁺ and N₁₃ ^– isomers have been investigated with second-order Møller–Plesset (MP2) and density functional theory (DFT) methods. Five N₁₃ ⁺ isomers and six N₁₃ ^– isomers are all reasonable local minima on their potential energy hypersurfaces. The most stable N₁₃ ⁺ cation is structure C-2 with C_2v symmetry, which contains a pentazole ring and two N₄ open chains. It is different from those of the N₇ ⁺ and N₉ ⁺ clusters, but similar to the N₁₁ ⁺ cluster. Meanwhile, the most stable N₁₃ ^– structure A-2 is composed of a pentazole ring and a six-membered ring connected by two nitrogen atoms. It is not only different from those of the N₇ ^– and N₉ ^– clusters, but also from the N₁₁ ^– cluster. The decomposition pathways of structures C-2 and A-2 were investigated at the B3LYP/(aug)-cc-pVDZ level. From the barrier heights of the structures C-2 and A-2 decomposition processes, it is suggested that C-2 is difficult to observe experimentally and A-2 may be observed as a short-lived species. Figure Optimized geometrical parameters of N₁₃ ⁺ isomer C-2      

Tunicamycin-induced alterations in the synthesis of sulfated proteoglycans and cell surface morphology in the chick embryo fibroblast

The effect of tunicamycin (TM) on the synthesis and secretion of sulfated proteoglycans and hyaluronate was examined in chick embryo fibroblasts and chondrocytes. The incorporation of the precursors [³H]glucosamine, [³H]mannose and [³⁵S]sulfate into glycoconjugates in both the cell layer and medium of cultures was determined. In the chick embryo fibroblast, but not in the chondrocyte, synthesis of sulfated proteoglycan was inhibited 60–75% by TM (5 × 10⁻⁸ M), while synthesis of hyaluronate and protein was only inhibited slightly. The inhibition of sulfate incorporation into glycosaminoglycans of the chick embryo fibroblast was overcome to a great extent by addition of β-xyloside, which provides an exogenous initiator for chondroitin sulfate synthesis. TM treatment also altered cell shape and surface morphology in chick embryo fibroblasts, as observed by phase contrast and scanning electron microscopy (SEM). Cells treated with TM became rounded, and increased numbers of microvilli and blebs appeared on the cell surface. These alterations in cell morphology were reversed by removal of TM, but not by exogenous addition of xyloside, chondroitin sulfate or the adhesive cell surface glycoprotein fibronectin. These results demonstrate that TM inhibits synthesis of sulfated proteoglycans in the chick embryo fibroblast and causes a dramatic alteration in cell shape and surface morphology.     

Biophysical and biochemical characterization of recombinant human Pop2 deadenylase

Pop2, a component of the Ccr4–Not complex, functions as a deadenylase both in vitro and in vivo. In this research, we found that the recombinant human Pop2 (hPop2) mainly existed in a compact monomeric state with a α + β tertiary structure type. The percentages of the secondary structures evaluated from the CD spectrum were about 37% α-helix, 14% β-sheet, and 19% β-turns. The optimal condition for hPop2 catalysis was pH 7–8 at 37 °C. Mg²⁺, Mn²⁺, and Co²⁺ had similar effects on the deadenylation activity of hPop2, and the optimal concentration was 0.3–0.5 mM. The deadenylase activity of hPop2 was, at least partially, specific when coordinated with divalent metal ions. The enzyme was not inhibited much by the nucleotide analogs, and the product 5′-AMP was the most efficient inhibitor. The dissimilarity in the metal ion dependence and inhibitory effects of the nucleotide analogs suggested that various deadenylases might have differential regulation mechanisms.     

The impacts of re-introducing Mississippi River water on the hydrologic budget and nutrient inputs of a deltaic estuary

Most wetlands of the Mississippi deltaic plain are isolated from riverine input due to flood control levees along the Mississippi River. These levees have altered hydrology and ecology and are a primary cause of massive wetland loss in the delta. River water is being re-introduced into coastal basins as part of a large-scale ecological engineering effort to restore the delta. We quantified freshwater, nitrogen, and phosphorus inputs to the Breton Sound Estuary for three climatically different years (2000, 2001, and 2002). Water budgets included precipitation, potential evapotranspiration, the diversion, stormwater pumps, and groundwater. Precipitation contributed 48–57% of freshwater input, while the diversion accounted for 33–48%. Net groundwater input accounted for less than 0.05% of freshwater inputs. Inputs of ammonium (NH₄-N), nitrate (NO₃-N), total nitrogen (TN), and total phosphorus (TP) were determined for each of the water sources. Atmospheric deposition was the most important input of NH₄-N (57–62% or 1.44 × 10⁵–2.32 × 10⁵ kg yr⁻¹) followed by the diversion. The diversion was the greatest source of NO₃-N (67–83%, 7.78 × 10⁵–1.64 × 10⁶ kg yr⁻¹) and TN (60–71%). The diversion contributed 41–60% of TP input (1.17 × 10⁵–2.32 × 10⁵ kg yr⁻¹). Annual loading rates of NH₄-N and NO₃-N were 0.17–0.27 and 1.2–2.3 g N m⁻² yr⁻¹, respectively, for the total basin indicating strong retention of nitrogen in the basin. Nitrogen retention through denitrification and burial was estimated for the upper basin.     

Hydrolysis of the amide bond in methionine-containing peptides catalyzed by various palladium(II) complexes: Dependence of the hydrolysis rate on the steric bulk of the catalyst

¹H NMR spectroscopy was applied to study the reactions of cis-[Pd(L)(H₂O)₂]²⁺ complexes (L is en, pic and dpa) with the N-acetylated tripeptides L-methionylglycylglycine, MeCOMet–Gly–Gly, and glycyl–L-methionyl–glycine, MeCOGly–Met–Gly. All reactions were performed in the pH range 2.0–2.5 with equimolar amounts of the cis-[Pd(L)(H₂O)₂]²⁺ complex and the tripeptide at 60 °C. The hydrolytic reactions of the cis-[Pd(en)(H₂O)₂]²⁺, cis-[Pd(pic)(H₂O)₂]²⁺ and cis-[Pd(dpa)(H₂O)₂]²⁺ complexes with MeCOMet–Gly–Gly were regioselective and only the amide bond involving the carboxylic group of methionine was cleaved. However, in the reactions of these three Pd(II) complexes with MeCOGly–Met–Gly, two amide bonds, Met–Gly and MeCO–Gly, were cleaved. From UV–Vis spectrophotometry studies, it was found that the rate-determining step of these hydrolytic reactions is the monodentate coordination of the corresponding Pd(II) complex to the sulfur atom of the methionine side chain. The rate of the cleavage of these amide bonds is dependent on the nature of the bidentate coordinated diamine ligand L (en > pic > dpa). The hydrolytic reaction of cis-[Pd(L)(H₂O)₂]²⁺-type complexes with MeCOMet–Gly–Gly, containing the methionine side chain in the terminal position of the peptide, is regioselective while in the reaction of these Pd(II) complexes with MeCOGly–Met–Gly, none selective cleavage of the peptide occurs. This study contributes to a better understanding of the selective cleavage of methionine-containing peptides employing palladium(II) complexes as catalysts.     

Biosorption of nonylphenol on dead biomass of Rhizopus arrhizus encapsulated in chitosan beads

The nonylphenol (NP) biosorption and desorption potential for fungal biomass used under batch conditions was investigated using kinetics and isotherm models. Fungal biomass of Rhizopus arrhizus TISTR 3610 exhibited preferential uptake of NP, an endocrine disrupting chemicals. Sporangiospores, asexual spores, were immobilised in chitosan beads. The biosorption data of NP on the moist heat inactivated R. arrhizus–chitosan beads were analyzed using four popular adsorption isotherms and, by using non-linear least-regression with the solver add-in in Microsoft Excel, correlated in order with the Fritz–Schluender > Redlich–Peterson > Freundlich > Langmuir isotherms. The pseudo first-order kinetics was found to have the best fit with the experimental data. The diffusivity of NP in the R. arrhizus–chitosan beads was calculated using the shrinking core model, and the diffusivity values were in the ranges of 2.3736 × 10⁻⁴–1.8950 × 10⁻⁴ cm² s⁻¹. Desorption to recover the adsorbed NP from the beads was performed in methanol and was best described using a pseudo second-order kinetic model.     

ICChI, a glycosylated chitinase from the latex of Ipomoea carnea

A multi-functional enzyme ICChI with chitinase/lysozyme/exochitinase activity from the latex of Ipomoea carnea subsp. fistulosa was purified to homogeneity using ammonium sulphate precipitation, hydrophobic interaction and size exclusion chromatography. The enzyme is glycosylated (14–15%), has a molecular mass of 34.94 kDa (MALDI–TOF) and an isoelectric point of pH 5.3. The enzyme is stable in pH range 5.0–9.0, 80 °C and the optimal activity is observed at pH 6.0 and 60 °C. Using p-nitrophenyl-N-acetyl-β-d-glucosaminide, the kinetic parameters K_m, V_max, K_cat and specificity constant of the enzyme were calculated as 0.5 mM, 2.5 × 10⁻⁸ mol min⁻¹ μg enzyme⁻¹, 29.0 s⁻¹ and 58.0 mM⁻¹ s⁻¹ respectively. The extinction coefficient was estimated as 20.56 M⁻¹ cm⁻¹. The protein contains eight tryptophan, 20 tyrosine and six cysteine residues forming three disulfide bridges. The polyclonal antibodies raised and immunodiffusion suggests that the antigenic determinants of ICChI are unique. The first fifteen N-terminal residues G–E–I–A–I–Y–W–G–Q–N–G–G–E–G–S exhibited considerable similarity to other known chitinases. Owing to these unique properties the reported enzyme would find applications in agricultural, pharmaceutical, biomedical and biotechnological fields.