Influence of drying on the liquid limit behaviour of a marine clay

The possible mechanisms of particle aggregation and reduction in liquid limit of the Cochin marine clay on drying are investigated. Mineralogical analysis showed the absence of halloysite in the marine specimen. Experimental results also ruled out the possibility of cementitious material being responsible for particle aggregation and reduction in clay plasticity on drying. The presence of calcium and magnesium as the predominant exchangeable ions and of a high pore salt concentration facilitates strong interparticle attraction and small particle separations; the latter leads to development of significant capillary stresses that permits an intimate contact of particles and growth of strong van der Waals' and Coulombic bonds.

Purification and characterization of an alpha-D-glucuronidase from a thermophilic fungus, Thermoascus aurantiacus

An alpha-D-glucuronidase was purified from the culture filtrates of Thermoascus aurantiacus. A simple colorimetric method for its assay is reported. The enzyme is a single polypeptide chain with a molecular weight of 118,000. It acts optimally at pH 4.5. It shows maximum activity at 65 degrees C. The t 1/2 at 70 degrees C was 40 min. It specifically cleaved the alpha-(1----2) linkage between 4-O-methyl-alpha-D-glucuronic acid and the xylose residue in xylan and several glucurono-xylooligosaccharides.

Purification and properties of β-glucosidase from a thermophilic fungus Humicola lanuginosa (Griffon and Maublanc) Bunce

An extracellular β-glucosidase (EC 3.2.1.21) has been purified to homogeneity from the culture filtrate of a thermophilic fungus, Humicola lanuginosa (Griffon and Maublanc) Bunce, using duplicating paper as the carbon source. The enzyme was purified 82-fold with a 43% yield by ion-exchange chromatography and gel filtration. The molecular weight of the protein was estimated to be 135,000 by gel filtration and 110,000 by electrophoresis. The sedimentation coefficient was 10.5 S. It was an acidic protein containing high amounts of acidic amino acid residues. It was poor in sulphur-containing amino acids. It also contained 9% carbohydrate. The enzyme activity was optimum at pH 4.5 and at 60°C. The enzyme was stable in the pH range 6–9 for 24 h at 25°C. The enzyme had similar affinities towards cellobiose and p-nitrophenyl-β-d-glucoside with Km values of 0.44 mM and 0.50 mM, respectively. The enzyme was capable of hydrolysing larchwood xylan, xylobiose and p-nitrophenyl-β-d-xyloside, though to a lesser extent. The enzyme was specific for the β-configuration and glucose moiety in the substrate.

A study of geotechnical properties of Cochin Marine Clays

Most of the Greater Cochin area, which is undergoing rapid industrialisation, consists of extremely soft marine clay calling for expensive deep foundations. This paper presents a study on the physical properties and engeering characteristics of Cochin marine clays. These marine clays are characterised by high Atterberg limits and natural water contents. They are moderately sensitive with liquidity indices ranging over 0.46 to 0.87.The grain size distribution shows almost equal fractions of clay and silt size with sand content varying around 20%. Use of a dispersing agent in carrying out grain size distribution test plays an important role. The fabric of these clays had been identified as flocculant. The pore water has low salinity which results in marginal changes in properties on washing.Consolidation test results showed a preconsolidation pressure of up to about 0.5 kg/cm2 with high compression indices. Compression index vs liquid limit yielded a correlation comparable to that of published data. The undisturbed samples have a much larger coefficient of secondary consolidation as a result of flocculant fabric. These clays have very low undrained shear strength.

Purification and properties of trehalase from the thermophilic fungus Humicola lanuginosa

Trehalase (?,?-Trehalosee gludohydrolase, EC 3.2.1.28) was partially solubilized from the thermophilic fungus Humicola lanuginosa RM-B, and purified 184-fold. The purified enzyme was optimally active at 50°C in acetate buffer at pH 5.5. It was highly specific for ?,?-trehalose and had an apparent Km = 0.4 mM at 50°C. None of the other disaccharides tested either inhibited or activated the enzyme. The molecular weight of the enzyme was around 170000. Trehalase from mycelium grown at 40 and 50°C had similar properties. The purified enzyme, in contrast to that in the crude-cell free extract, was less stable. At low concentration, purified trehalase was afforded protection against heat-inactivation by �protective factor(s)� present in mycelial extracts. The �protective factor(s)� was sensitive to proteolytic digestion. It was not diffusable and was stable to boiling for at least 30 min. Bovine serum albumin and casein also protected the enzyme from heat-inactivation.

Effect of Temperature on Respiration of a Mesophilic and a Thermophilic Fungus

The respiratory rates of mycelia of the mesophilic fungus, Aspergillus niger, and the thermophilic fungus, Thermomyces lanuginosus, were comparable at their respective temperature optima for growth. The respiratory rate of A. niger was independent of changes in temperature between 15 and 40 C. The respiratory rate of T. lanuginosus increased with increase in temperature between 25 and 55 C.

Temperature response of trehalase from a mesophilic (Neurospora crassa) and a thermophilic (Thermomyces lanuginosus) fungus

The purified trehalases of the mesophilic fungus, Neurospora crassa, and the thermophilic fungus, Thermomyces lanuginosus, had similar temperature and pH optima for activity, but differed in molecular weight, electrophoretic mobility and Michaelis constant. At lower concentration, trehalases from both fungi were inactivated to similar extent at 60°C. While purified trehalase of T. lanuginosus was afforded protection against heat-inactivation by proteinaceous protective factor(s) present in mycelial extracts, by bovine serum albumin and by casein, these did not afford protection to N. crassa trehalase against heat inactivation. Both trehalases exhibited discontinuous Arrhenius plots with temperature of discontinuity at 40°C. The activation energy calculated from the slope of the Arrhenius plot was higher for the T. lanuginosus enzyme. The plots of apparent K m versus 1/T for trehalases of N. crassa and T. lanuginosus were linear from 30° to 60°C. The results show that purified trehalases of the mesophilic and the thermophilic fungus are distinct. Although, these exhibit similar thermostability of their catalytic function at low concentration, distinctive thermal stability characteristics of thermophilic enzyme become apparent at high protein concentration. This could be brought about in the cell by the enzyme itself, or by other proteins.

Two Novel Hexadepsipeptides with Several Modified Amino Acid Residues Isolated from the Fungus

Two new cyclohexadepsipeptides have been isolated from the fungus Isaria. Fungal growth in solid media yielded hyphal strands from which peptide fractions were readily isolable by organic-solvent extraction. Two novel cyclodepsipeptides, isaridin A and isaridin B, have been isolated by reverse-phase HPLC, and characterized by ESI-MS and 1H-NMR. Single crystals of both peptides have been obtained, and their 3D structures were elucidated by X-ray diffraction. The isaridins contain several unusual amino acid residues. The sequences are cyclo(β-Gly-HyLeu-Pro-Phe-NMeVal-NMePhe) and cyclo(β-Gly-HyLeu-β-MePro-Phe-NMeVal-NMePhe), where NMeVal is N-methylvaline, NMePhe N-methylphenylalanine, and HyLeu hydroxyleucine (=2-hydroxy-4-methylpentanoic acid). The two peptides differ from one another at residue 3, isaridin A having an (S)-proline at this position, while β-methyl-(S)-proline (=(2S,3S)-2,3,4,5-tetrahydro-3-methyl-1H-pyrrole-2-carboxylic acid) is found in isaridin B. The solid-state conformations of both cyclic depsipeptides are characterized by the presence of two cis peptide bonds at HyLeu(2)-Pro(3)/HyLeu(2)-β-MePro(3) and NMeVal(5)-NMePhe(6), respectively. In isaridin A, a strong intramolecular H-bond is observed between Phe(4)CO⋅⋅⋅HNβ-Gly(1), and a similar, but weaker, interaction is observed between β-Gly(1)CO⋅⋅⋅HNPhe(4). In contrast, in isaridin B, only a single intramolecular H-bond is observed between β-Gly(1)CO⋅⋅⋅HNPhe(4

Identification and characterization of a library of microheterogeneous cyclohexa-depsipeptides from the fungus

Ten new cyclic hexadepsipeptides, six isariins and four isaridins, from the fungus Isaria have been identified and characterized by high-performance liquid chromatography, coupled to tandem electrospray ionization mass spectrometry (LC-ESIMS/MS). The isariins possess a beta-hydroxy acid residue and five alpha-amino acids, while isaridins contain a beta-amino acid, an alpha-hydroxy acid, and four alpha-amino acids. One- and two-dimensional NMR spectroscopy confirmed the chemical identity of some of the isariin fractions. Mass spectral fragmentation patterns of [M + H](+) ions reveal clear diagnostic fragment ions for the isariins and isaridins. Previously described cyclic depsipeptides, isarfelins from Isaria felina (Guo, Y. X.; Liu, Q. H.; Ng, T. B.; Wang H. X. Peptides 2005, 26, 2384), are now reassigned as members of the isaridin family. Examination of isaridin sequences revealed significant similarities with cyclic hexadepsipeptides such as destruxins and roseotoxins. The structure of an isariin (isariin A) investigated by NMR spectroscopy indicated the presence of a hybrid alpha beta C-11 turn, formed by the beta-hydroxy acid and glycine residues and a (D)Leu-(L)Ala type II' beta-turn. Additionally, the inhibitory effect of isariins and an isaridin on the intra-erythrocytic growth of Plasmodium falciparum is presented.

Purification and properties of xylanase from the thermophilic fungus, Humicola lanuginosa (Griffon and Maublanc) Bunce

An extracellular xylanase was purified to homogeneity from the culture filtrate of the thermophilic fungus, Humicola lanuginosa (Griffon and Maublanc) Bunce and its properties were studied. A fourfold purification and a yield of 8% were achieved. The molecular-weight of the protein was found to be 22,500 based on electrophoretic mobility and 29,000 by gel filtration behavior. The protein is rich in acidic amino acids, glycine and tyrosine, and poor in sulfur-containing amino acids. The kinetic properties of the enzyme are similar to those of other fungal xylanases. The enzyme shows high affinity toward larchwood xylan (Km = 0.91 mg/ml) and hydrolyzes only xylan. The enzyme becomes inactivated when stored for more than 2 months at −20 °C in the dry state. Such an inactivation has not been reported so far for any xylanase. Using chromatographic techniques, one species of protein differing from the native protein in charge but enzymatically active was isolated in low yields. However, a large molecular-weight species of the protein devoid of enzyme activity was isolated in substantial quantities and further characterized. Based on ultracentrifugation and gel electrophoretic studies, it was concluded that this species may be an aggregate of the native protein and that such an aggregation might be taking place on storage in the dry state at −20 °C, leading to loss in activity.