Characterization of the 1 alpha,25-dihydroxyvitamin D3 receptor from rat intestinal cytosol.

The 1 alpha,25-dihydroxyvitamin D3 receptor from rat intestinal cytosol has been partially characterized. Sucrose density gradient sedimentation and analytical gel filtration analyses of this receptor yielded values of 3.1 S, 80,000, and 36 A for the sedimentation coefficient, molecular weight (Mr), and Stokes molecular radius (Rs), respectively. The receptor was found to be a protein by its susceptibility to protease but not nuclease digestion, and studies with N-ethylmaleimide and iodoacetamide revealed the presence of a reduced cysteine residue near the ligand binding site of the receptor. Kinetic and equilibrium binding studies showed an equilibrium dissociation constant of 7.4 x 10(-10) M (4 degrees C), an association rate constant of 1.7 x 10(7) M-1 min-1 (0 degrees C) and a dissociation rate constant of 7.2 x 10(-4) min-1 (4 degrees C, t1/2 = 16 h).     

Kinetics of hyaluronan hydrolysis in acidic solution at various pH values

Hyaluronic acid (HA) was hydrolyzed using varying temperatures (40, 60, and 80 degrees C) and acid concentrations (0.0010, 0.010, 0.10, 0.50, 1.0, and 2.0 M HCl). The degradation process was monitored by determination of weight average molecular weight ( M w) by size-exclusion chromatography with online multiangle laser light scattering, refractive index, and intrinsic viscosity detectors (SEC-MALLS-RI-visc) on samples taken out continuously during the hydrolysis. SEC-MALLS-RI-visc showed that the degradation gave narrow molecular weight distributions with polydispersity indexes ( M w/ M n) of 1.3-1.7. Kinetic plots of 1/ M w versus time gave linear plots showing that acid hydrolysis of HA is a random process and that it follows a first order kinetics. For hydrolysis in HCl at 60 and 80 degrees C, it was shown that the kinetic rate constant ( k h) for the degradation depended linearly on the acid concentration. Further, the dependence of temperature on the hydrolysis in 0.1 M HCl was found to give a linear Arrhenius plot (ln k h vs 1/ T), with an activation energy ( E a) of 137 kJ/mol and Arrhenius constant ( A) of 7.86 x 10 (15) h (-1). (1)H NMR spectroscopy was used to characterize the product of extensive hydrolysis (48 h at 60 degrees C in 0.1 M HCl). No indication of de- N-acetylation of the N-acetyl glucosamine (GlcNAc) units or other byproducts were seen. Additionally, a low molecular weight HA was hydrolyzed in 0.1 M DCl for 4 h at 80 degrees C. It was shown that it was primarily the beta-(1-->4)-linkage between GlcNAc and glucuronic acid (GlcA) that was cleaved during hydrolysis at pH < p K a,GlcA. The dependence of the hydrolysis rate constant was further studied as a function of pH between -0.3 and 5. The degradation was found to be random (linear kinetic plots) over the entire pH range studied. Further, the kinetic rate constant was found to depend linearly on pH in the region -0.3 to 3. Above this pH (around the p K a of HA), the kinetic constant decreased more slowly, probably due to either a change in polymer conformation or due to an increased affinity for protons due to the polymer becoming charged as the GlcA units dissociated.     

Properties of human serum low density lipoproteins after modification by succinic anhydride

Human serum low density lipoprotein of d 1.019-1.063 (LDL(2)) treated with succinic anhydride at pH 7.5-8.0 showed the same chemical composition, hydrodynamic properties (flotation and sedimentation coefficients, intrinsic viscosity) and optical properties (circular dichroism) as untreated LDL(2). However, in contrast to LDL(2), the succinylated product (s-LDL(2)) failed to react with rabbit anti-LDL(2) antisera. Extraction with ethanol-ether 3:1 yielded the succinylated apoprotein (s-apo-LDL(2)), which was, unlike untreated apoprotein, soluble in aqueous buffers. Succinylated apoprotein, which was also immunologically unreactive, appeared to differ in structure from s-LDL(2), as assessed by the parameters of intrinsic viscosity and circular dichroism. The molecular weights of both LDL(2) and s-LDL(2) obtained by the technique of sedimentation equilibrium were 2.1-2.3 x 10(6). By the same method, s-apo-LDL(2) gave an uncorrected figure of 3.95-4.15 x 10(4) and, after correction for succinyl functions, of 3.60-3.80 x 10(4). Because of the assumptions made in the computations, the latter figure was considered approximate. The marked differences in molecular weight between s-apo-LDL(2) and whole apo-LDL(2) ( approximately 5 x 10(5)) were taken to support the subunit structure of apo-LDL(2), which is envisaged as an aggregate of about 12 subunits which dissociate upon succinylation. Further, the large percentage (about 90%) of the free amino groups of LDL(2) found to react with succinic anhydride suggests that these groups are at the surface of the molecule.     

Molecular and catalytic properties of angiotensin converting enzyme-I from bovine seminal plasma

Angiotensin converting enzyme [EC 3.4.15.1] was shown to exist in two distinct forms in bovine seminal plasma. The higher molecular weight form of the enzyme (angiotensin convering enzyme I) was purified to homogeneity by Sephadex G-200 gel filtration, and DEAE-Sepharose, blue Sepharose, and concanavalin A-Sepharose column chromatography. Final recovery of the enzyme was 9.0. The molecular weight of the enzyme was estimated to be 8 x 10(5) by the gel filtration method. A value of 4.6 x 10(5) was obtained for the reduced and denatured enzyme by dodecylsulfate polyacrylamide gel electrophoresis. The Stokes' radius, diffusion coefficient, and intrinsic viscosity of the purified enzyme were determined to be 95 A, 2.3 x 10(-7) cm2/s, and 6.76 ml/g. The enzyme had a specific activity of 105.12 mumol/min/mg protein for hippurylhistidylleucine. The Km value for hippurylhistidylleucine was found to be 20 mM. Studies with EDTA suggest that metal ions which are tightly bound are required for its activity. The enzyme was inhibited by some heavy metal ions but did not required sulfhydryl groups for its activity. Trypsin treatment of the urea-denatured enzyme produced a catalytically active fragment with an Mr of 30,000. Chemical hydrolysis of the native enzyme did not produce any active fragment.     

Physical properties of Artemia salina ribosomes.

Eukaryotic ribosomes were isolated from the cryptobiotic embryos and from the further-developed free-swimming nauplii of the brine shrimp Artemia salina. Analytical boundary sedimentation and photon correlation spectroscopy yielded, respectively, the standard sedimentation and diffusion coefficients at infinite dilution, s degrees 20,w = 81 +/- 1 S and D degrees 20,w = (1.41 +/- 0.02) x 10(-7) cm2/s, for the unfixed and formaldehyde-fixed ribosomes from different developmental stages and for ribosomes attached to a messenger RNA fragment. Also, the density increment was determined, from which the partial specific volume was derived (0.63 +/- 0.01 cm3/g). Combination of the different measured parameters gives accurate values for the molecular weight (3.8 +/- 0.1) x 106 and for size and solvation parameters. These results are compared with their counterparts for the smaller ribosomes from the prokaryote Escherichia coli.     

Physicochemical properties of pyocin F1.

The physiochemical properties of pyocin F1 were studied. Pyocin F1 consists of flexuous rod-like particles homogenous in size. Each particle was composed of rod and fiber parts. The rod part was 105.5 +/- 9.5 nm long and 10.0 +/- 1.4 nm wide, and showed regular striations amounting to 23 layers. The fiber part was composed of several filaments; the length of the longest filament was 43.0 +/- 12.0 nm. The amino acid composition, the partial specific volume (0.720 ml/g), the sedimentation coefficient (S020,W = 35.1S), and the translational diffusion constant (0.94 +/- 0.01 x 10(-7) cm2/s) were determined. The particle weight was calculated to be 3.23 x 10(6) daltons.     

Molecular Weight Determination of Sendai and Newcastle Disease Virus RNA

The molecular weights of Sendai and Newcastle disease virus RNA were estimated by sedimentation in sucrose gradients and by length measurements in the electron microscope under both denaturing and nondenaturing conditions. Sedimentation analyses under denaturing conditions yielded molecular weight estimates of 2.3 x 10(6) to 2.6 x 10(6), whereas length measurements yielded estimates of 5.2 x 10(6) to 5.6 x 10(6) for both denatured and nondenatured viral RNA. It would appear that the conditions of denaturation used (99% dimethyl sulfoxide at 26 C, and reaction with 1.1 M formaldehyde for 10 min at 60 C) do not equally denature parainfluenza virus RNA and other RNAs, such as cellular rRNA, 45S rRNA precursor, and R17 RNA.     

Kinetic analysis of glycine and glycylglycine absorption in rat small intestine in chronic experiment

Kinetics of glycylglycine hydrolysis and absorption as well as that of free glycine absorption in isolated loop of the small intestine was studied in chronic experiments in two groups of rats. In the 1st group (n = 5), the isolated loop daily received for 1 or two hours a glucose load (25 mM), whereas in the 2nd group (n = 4)--a glutamic acid load (25 mM). The "true" values (i.e. corrected for the influence of the pre-epithelial layer) of the Michaelis constant for dipeptide transport were lower than those for the free glycine transport: 16 +/- 1.8 versus 36.3 +/- 3.7 mM (in the 1st group) and 15.9 +/- 2.2 versus 34.0 +/- 3.7 mM (in the 2nd group), whereas values of the maximal rate of active transport as calculated per 1 cm of the intestine length were, on the contrary, higher: 0.64 +/- 0.06 versus 0.42 +/- 0.10 mumol/(min.cm) 1st group and 0.86 +/- 0.13 versus 0.56 +/- 0.04 mumol/(min.cm) in the in the 2nd group. It has been shown that, under these conditions, regarded as the most physiological, over 90% of glycylglycine is absorbed via the peptide transport system. Only a small part of this dipeptide amount (less than 10%) splits during membrane hydrolysis with subsequent absorption of the derived glycine. It has also been found that glutamic acid solution as a regular substrate load is more effective (as compared with the glucose solution) in retarding the atrophic changes occurring in the isolated intestine loop and in preserving its structural and functional parameters on a higher level.     

ATP Sulfurylase from Penicillium chrysogenum: Is the Internal Level of the Enzyme Sufficient to Account for the Rate of Sulfate Utilization?

The in vivo rate of sulfate activation in Penicillium chrysogenum (wild-type strain ATCC 24791) was determined to be 0.19 +/- 0.09 mumol g(-1) (dry weight) min(-1) by the following methods. (i) The maximum growth of the organism in synthetic medium was a linear function of the initial Na(2)SO(4) concentration between 0 and 8 x 10(-4) Na(2)SO(4). The growth yield was 1.64 x 10(-2) g (dry weight) of mycelium per mumol of added sulfate, corresponding to a minimum sulfur requirement of 61 mumol/g (dry weight). Under these conditions (limiting sulfate) the minimum doubling time of P. chrysogenum in submerged culture was about 3.8 h, corresponding to a maximum exponential growth rate constant of 3.0 x 10(-3) min(-1). If all the sulfur in this mycelium passed through adenosine-5'-phosphosulfate, the rate of sulfate activation in vivo must have been 0.183 mumol min(-1) g(-1) (dry weight). (ii) In the presence of excess (35)SO(4) (2-), the total organic (35)S produced varied with the mycelial growth rate. However, until the culture approached maximum density, the product of [(growth rate constant) x (organic (35)S content)] was nearly constant at 0.24 to 0.28 mumol min(-1) g(-1) (dry weight). (iii) A sulfur-starved mycelium pulsed with 10(-4) M (35)SO(4) (2-) produced organic (35)S at a rate of about 0.10 mumol min(-1) g(-1) (dry weight) under conditions where the internal concentrations of ATP and sulfate would permit ATP sulfurylase to operate at about 70% of its V(max). Cell-free extracts of P. chrysogenum growing rapidly on excess sulfate contained 0.22 U of ATP sulfurylase per g (dry weight). Thus, in spite of the relatively low specific activity of homogeneous ATP sulfurylase (0.13 U/mg of protein, corresponding to an active site turnover of 7.15 min(-1)), the mycelial content of the enzyme was sufficient to account for the observed growth rate of the organism on inorganic sulfate as the sole sulfur source.     

A field study into the appropriateness of transcutaneous ultrasonography in the diagnoses of uterine disorders in reproductively failed pigs

This study was conducted to define the characteristics of the uterus of reproductively failed pigs by transcutaneous ultrasonography (SONO) in order to investigate the appropriateness of SONO to diagnose presumptive uterine disorders. Zearalenone (ZEA) is known to affect uterine function and causes endometrial liquid accumulation and was also determined. In 33 sows and 14 gilts, of unknown reproductive stages and culled for failing to conceive, the uterus was scanned transcutaneously and the females slaughtered on the same day or the day after scanning. Parameters determined by SONO were uterine echotexture (UET; graded 1 for homogeneous to 4 for highly heterogeneous), uterine size (US; expressed as the mean sectional area of two to three cross-sections of the uterine horns given in cm2) and intrauterine content. Post mortem, the ovarian structures were assessed and females grouped accordingly into those in estrus (n=2), early diestrus (n=14), diestrus (n=15), late diestrus (n=1), anestrus (n=10) and having polycystic ovarian degeneration (n=5). The uterine weight (UW) was recorded and uterine specimens microscopically evaluated for an endometrial oedema (EO; grades 1 for none, to 4, if an oedema was clearly evident) and for immune cells to assess endometritis. Total ZEA was analysed in bile and females with >or=50 ng/ml judged as positive. The uterus could be examined in all animals. UET, US, UW and EO was found to be different between groups, and a positive correlation (P<0.001) established for US and UET (r=0.71), US and EO (r=0.51), UET and EO (r=0.57), US and UW (UW=357.6 x US(0.801); r=0.88). One female had intrauterine fluid and an acute-chronic endometritis diagnosed. Almost all females had a chronic endometritis and a majority found ZEA positive. No differences were observed between groups and a relationship between ZEA or chronic endometritis and UET, US, UW and EO were not established. In conclusion, transcutaneous SONO is appropriate to examine the uterus in reproductively failed pigs on farms, and the estimation of UET and US gives information on EO and UW. Intrauterine fluid is indicative for a severe uterine inflammation. Since groups differed in UET and US, but were equally ZEA positive and the uteri chronically inflamed, an UET and US specifically associated with ZEA or chronic endometritis is questioned.     

Purification and Properties of a Glycoprotein Acid Phosphatase from Candida albicans

An acid phosphomonoesterase was purified 87-fold with a 4% recovery from disintegrated cells of Candida albicans by four stages of column chromatography. The purified enzyme was homogeneous by ultracentrifugal, electrophoretic, and immunological analyses. The fully corrected sedimentation coefficient, s(20,w), was calculated to be 5.51s. Molecular weight estimated from ultracentrifugal data was 124.3 x 10(3), from gel chromatography was 115 x 10(3), and from acrylamide gel electrophoretic data was 131 x 10(3). Buoyant density in sucrose was 1.15 g/cm(3). The enzyme was a mannoprotein with a hexose to protein ratio of 7: 1. The Michaelis constant of the enzyme was 3.3 x 10(-4) M for p-nitrophenyl phosphate as substrate, and the pH optimum was 4.5. The enzyme was competitively inhibited by inorganic phosphate (K(i) = 10(-4) M) and by arsenate (K(i) = 0.5 x 10(-4) M). A wide range of inorganic cations and anions did not affect enzyme activity, but Hg(2+), Cd(2+), and Cu(2+) were inhibitory. F(-) was also inhibitory at low concentrations, but the effect was reversed at higher concentrations. Phosphatase activity was completely destroyed by exposure of the enzyme to 70 C for 12 min, but was destroyed only slowly by proteolytic hydrolysis. The purified glycoprotein enzyme gave a line of identity with the "b" antigen of crude C. albicans homogenates in immunodiffusion and immunoelectrophoresis tests with sera from rabbits inoculated with intact C. albicans cells and from humans with proven candidiasis. Preliminary evidence suggests that the mannan and not the protein portion of the enzyme molecule is responsible for this antigenicity.     

Theoretical and experimental studies on viscoelastic properties of erythrocyte membrane.

The deformation of a portion of erythrocyte during aspirational entry into a micropipette has been analyzed on the basis of a constant area deformation of an infinite plane membrane into a cylindrical tube. Consideration of the equilibrium of the membrane at the tip of the pipette has generated the relation between the aspirated length and the dimensionless time during deformational entry as well as during relaxation after the removal of aspiration pressure. Experimental studies on deformation and relaxation of normal human erythrocytes were performed with the use of micropipettes and a video dimension analyzer which allowed the continuous recording of the time-courses. The deformation consisted of an initial rapid phase with a membrane viscosity (range 0.6 x 10(-4) to 4 x 10(-4) dyn.s/cm) varying inversely with the degree of deformation and a later slow phase with a high membrane viscosity (mean 2.06 x 10(-2) dyn.s/cm) which was not correlated with the degree of deformation. The membrane viscosity of the recovery phase after 20 s of deformation (mean 5.44 x 10(-4) dyn.s/cm) was also independent of the degree of deformation. When determined after a short period of deformation (e.g., 2 s), however, membrane viscosity of the recovery phase became lower and agreed with that of the deformation phase. These results suggest that the rheological properties of the membrane can undergo dynamic changes depending on the extent and duration of deformation, reflecting molecular rearrangement in response to membrane strain.     

In vitro hydrolysis of blends from enantiomeric poly(lactide)s. 3. Homocrystallized and amorphous blend films

Homocrystallized and amorphous enantiomeric blend films were prepared from the melt of high molecular weight poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) (1:1) by crystallization and quenching, respectively. A phosphate-buffered solution was used to investigate effects of homocrystallinity via in vitro hydrolysis as well as crystallization process during the hydrolysis, which was performed for a period of 24 months at 37 degrees C and pH 7.4. Results derived from gravimetry, gel permeation chromatography, and tensile testing showed that hydrolyzability was higher for the homocrystallized film than for the amorphous film. Thus, probable mechanisms are proposed for the enhanced hydrolysis of the homocrystallized blend film compared with that of the amorphous blend film. The hydrolysis rate constant (k) values of the homocrystallized and amorphous films estimated from the changes in number-average molecular weight (M(n)) were 5.00 x 10(-3) and 3.32 x 10(-3) day(-1), respectively. Moreover, hydrolyzability of equimolar enantiomeric poly(lactic acid) blends can be altered in the k range of 0.73 x 10(-3) and 5.00 x 10(-3) day(-1) by varying their crystalline species, crystallinity, or molecular weights.     

The purification and properties of isocitrate lyase from Chlorella

1. Isocitrate lyase (threo-d(s)-isocitrate glyoxylate-lyase, EC 4.1.3.1) has been purified from acetate-adapted cells of Chlorella pyrenoidosa. 2. The final preparation was homogeneous by the criteria of sedimentation, diffusion and polyacrylamide-gel electrophoresis. 3. The sedimentation coefficient (S(20,w)) was 9.04x10(-13)sec. and the diffusion coefficient (D(20,w)) 4.62x10(-7)cm.(2)/sec.; from these values the molecular weight of the enzyme was calculated to be 170000 and its Stokes radius to be 4.63x10(-7)cm. 4. The elution of the enzyme from Sephadex G-100 was studied and estimates of molecular weight and Stokes radius were obtained from the elution data. 5. The turnover number of the enzyme was 5950moles of glyoxylate formed/min./mole of enzyme at 30 degrees . 6. With threo-d(s)(+)-isocitrate as substrate, the K(m) of the enzyme was 0.023mm.     

颗粒状固定化青霉素酰化酶的研究

将巨大芽孢杆菌 (Bacillusmegaterium)胞外青霉素酰化酶通过共价键结合到聚合物载体EupergitC颗粒环氧基团上 ,制成的颗粒状固定化青霉素酰化酶表现活力达 1 40 0 μ/g左右。固定化酶水解青霉素的最适 pH8 0 ,最适温度为 55℃。在pH6 0～ 8 5、温度低于 40℃时固定化酶活力稳定。在 pH8 0、温度 37℃时 ,固定化酶对青霉素的表现米氏常数Ka为 2×1 0 - 2 mol/L ;苯乙酸为竞争性抑制剂 ,抑制常数Kip为 2 8× 1 0 - 2 mol/L ;6 APA为非竞争性抑制剂 ,抑制常数Kia为 0 1 2 5mol/L。固定化酶水解青霉素 ,投料浓度为 8% ,在使用 2 0 0批后 ,保留活力 80 %左右 ,6 APA收率平均达 89 48%。     

Properties of fractionated chondroitin sulphate from ox nasal septa

1. Chondroitin sulphate was isolated from bovine nasal septa by precipitation with cetylpyridinium chloride after digestion of the tissue with papain. 2. The material was divided into two portions, one of which was partially degraded with testicular hyaluronidase. 3. Untreated and hyaluronidase-digested material were fractionated into a total of eleven subfractions by gel chromatography on Sephadex G-200 and Sephadex G-100 respectively. 4. Chemical analyses indicated that the composition of all the fractions was similar to that of chondroitin sulphate. However, electrophoresis revealed a charge-inhomogeneity in the low-molecular-weight fractions obtained after hyaluronidase digestion. 5. The physicochemical properties of the subfractions were investigated by sedimentation-velocity, diffusion and sedimentation-equilibrium studies, osmometry, viscometry and gel chromatography. The individual fractions were essentially monodisperse and showed molecular weights ranging from 2400 to 36000. 6. The relationship between the intrinsic viscosity and the molecular weight was [eta]=5.0x10(-6)xM(1.14), indicating that the chondroitin sulphate molecules assume a shape intermediate between that of a random coil and a stiff rod. 7. The relationship between the sedimentation constant and the molecular weight (>10(4)) was s(0) (20,w)=2.3x10(-2)xM(0.44).     

Size and Composition of Marek''s Disease Virus Deoxyribonucleic Acid

Deoxyribonucleic acid (DNA) extracted from purified nucleocapsids of Marek's disease herpesvirus (MDV) was cosedimented with T4 and with herpes simplex virus (HSV) DNA in neutral sucrose density gradients and with T4 DNA in alkaline sucrose density gradients. These experiments indicated that the intact MDV DNA had a sedimentation constant of 56S corresponding to a molecular weight of 1.2 x 10(8) daltons. In the alkaline gradients, the largest and most prominent band contains a DNA sedimenting at 70S corresponding to 6.0 x 10(7) daltons in molecular weight. The DNA is therefore double-stranded and not cross-linked. Isopycnic sedimentation of the MDV DNA molecules with SPO1, Micrococcus lysodeikticus, and HSV DNA gave a density of 1.705 g/cm(3) corresponding to 46 guanine plus cytosine moles per cent. Lastly, in hybridization tests the DNA hybridized with RNA of infected cells but not with that of uninfected cells supporting the conclusion that it is viral.     

High yield production of monomer-free chitosan oligosaccharides by pepsin catalyzed hydrolysis of a high deacetylation degree chitosan

The high molecular weight of chitosan, which results in a poor solubility at neutral pH values and high viscosity aqueous solutions, limits its potential uses in the fields of food, health and agriculture. However, most of these limitations are overcome by chitosan oligosaccharides obtained by enzymatic hydrolysis of the polymer. Several commercial enzymes with different original specificities were assayed for their ability to hydrolyze a 93% deacetylation degree chitosan and compared with a chitosanase. According to the patterns of viscosity decrease and reducing end formation, three enzymes--cellulase, pepsin and lipase A--were found to be particularly suitable for hydrolyzing chitosan at a level comparable to that achieved by chitosanase. Unlike the appreciable levels of both 2-amino-2-deoxy-D-glucose and 2-acetamido-2-deoxy-D-glucose monomers released from chitosan by the other enzymes after a 20h-hydrolysis (4.6-9.1% of the total product weight), no monomer could be detected following pepsin cleavage. As a result, pepsin produced a higher yield of chitosan oligosaccharides than the other enzymes: 52% versus as much as 46%, respectively. Low molecular weight chitosans accounted for the remaining 48% of hydrolysis products. The calculated average polymerization degree of the products released by pepsin was around 16 units after 20h of hydrolysis. This product pattern and yield are proposed to be related to the bond cleavage specificity of pepsin and the high deacetylation degree of chitosan used as substrate. The optimal reaction conditions for hydrolysis of chitosan by pepsin were 40 degrees C and pH 4.5, and an enzyme/substrate ratio of 1:100 (w/w) for reactions longer than 1h.     

Methylated sulfur compounds in microbial mats: in situ concentrations and metabolism by a colorless sulfur bacterium

The concentrations of the volatile organic sulfur compounds methanethiol, dimethyl disulfide, and dimethyl sulfide (DMS) and the viable population capable of DMS utilization in laminated microbial ecosystems were evaluated. Significant levels of DMS and dimethyl disulfide (maximum concentrations of 220 and 24 nmol cm3 of sediment-1, respectively) could be detected only at the top 20 mm of the microbial mat, whereas methanethiol was found only at depth horizons from 20 to 50 mm (maximum concentration of 42 nmol cm3 of sediment-1). DMS concentrations in the surface layer doubled after cold hydrolysis of its precursor, dimethylsulfoniopropionate. Most-probable-number counts revealed 2.2 x 10(5) cells cm3 of sediment-1, in the 0- to 5-mm depth horizon, capable of growth on DMS as the sole source of energy. An obligately chemolithoautotrophic bacillus designated strain T5 was isolated from the top layer of the marine sediment. Continuous culture studies in which DMS was the growth-limiting substrate revealed a maximum specific growth rate of 0.10 h-1 and a saturation constant of 90 mumol liter-1 for aerobic growth on this substrate.     

Physicochemical characterization of konjac glucomannan

Four commercial konjac glucomannan (KGM) samples and a glucomannan derived from yeast were characterized by aqueous gel permeation chromatography coupled with multi angle laser light scattering (GPC-MALLS). Disaggregation of aqueous glucomannan solutions through controlled use of a microwave bomb facilitated reproducible molar mass distribution determination alleviating the need for derivatization of the polymer or the use of aggressive solvents. Further characterization was undertaken by use of capillary viscometry and photon correlation spectroscopy (PCS). The weight average molecular masses (M(w)) determined were in the region of 9.0 +/- 1.0 x 10(5) g mol(-1) for KGM samples and 1.3 +/- 0.4 x 10(5) g mol(-1) for the yeast glucomannan. The values determined for KGM in aqueous solution are in agreement with those reported for KGM in aqueous cadoxen. The degradation of samples observed upon autoclaving has been quantified by GPC-MALLS and intrinsic viscosity determination, allowing comparison with reported Mark-Houwink parameters. Shear flow experiments were undertaken for a range of KGM solutions of concentration 0.05 to 2.0% using a combination of controlled stress and controlled strain rheometers. The concentration dependence of the zero shear specific viscosity was determined by analysis of the data using the Ellis model. The dependence of the zero shear specific viscosity on the coil overlap parameter was defined and interpretation discussed in terms of the Martin and Tuinier equations.