Effect of pH on enzyme stability in soils

The pH stability of urease, acid phosphatase, alkaline phosphatase and phosphodiesterase in soils was investigated by first incubating a soil sample at the indicated pH (1–13) for 24 h and then measuring the activity at its optimal pH under standardized conditions. Generally, the decline in enzyme activity in a pH-profile near the optimum pH range was due to a reversible reaction that involved ionization or deionization of acidic or basic groups in the active centre of the enzyme-protein. Irreversible inactivation of the enzyme was particularly evident at the lower and higher ranges of acidic and alkaline conditions. Results showed that the pH stability of soil enzymes was highly dependent on the soils being assayed. The variation among soils may be attributed to the diversity of vegetation, micro-organisms and soil fauna as sources contributing to the enzyme activity and to the protective sites which allowed entrapment of the enzyme within colloidal humus and organo-mineral complexes. Adherence of the enzyme-protein to the humic-clay fractions would allow some resistance to pH denaturation.     

Arsenic resistant microorganisms isolated from agricultural drainage water and evaporation pond sediments

Elevated levels of As in contaminated water and soil could pose a major threat to the environment. Relatively high levels of As have been reported in agricultural drainage water and in evaporation pond sediments in Kern County, California. The objective of this study was to enumerate and isolate As-resistant microorganisms from agricultural drainage water and evaporation pond sediments and to assess their tolerance to metals, metalloids and antibiotics. The culture medium was amended with arsenite (III), arsenate (V), methylarsonic acid (MAA), and dimethylarsinic acid (DMA). Among the water samples, As(V), MAA, and DMA added to the medium at concentrations from 0.1 to 1000 mg L^?1 showed no effect on the colony forming units (CFUs) compared with no As supplementation, while arsenite (III) (> 1.0 mg L^?1) inhibited the population. The sediments showed three trends: (i) no effect on CFUs in the presence of As(V) up to 1000 mg kg^?1, (ii) a decline in CFUs in the presence of > 100 mg kg^?1, As(III), and (iii) an increase in CFUs upon the addition of MAA or DMA at > 25 mg kg^?1, Arsenite (III) was much more toxic to the indigenous microflora than any other As species. Arsenite (III) inactivates many enzymes by having a high affinity for thiol groups of proteins. A plate diffusion method was used to assess the tolerance of the As-resistant bacteria to heavy metals, metalloids and antibiotics. Of 14 isolates tested, all were resistant to Co, Cu, Pb, Ni, Mo, Cr, Se(IV), Se(VI), As(III), As(V), Sb, Sn, and Ag (50 µg mL^?1). The most toxic trace elements were Cd followed by Hg>Te>Zn. Multiple antibiotic tolerance (resistance to 2 or more antibiotics) was found among 43% of the isolates. The As-resistant bacteria showed a high tolerance to metals and antibiotics.     

l-Asparaginase activity of soils

Summary A simple, precise, and sensitive method to assay l-asparaginase (l-asparagine amidohydrolase, EC 3.5.1.1) activity in soils is described. This method use steam distillation to determine the NH _inf4 ^sup+ produced by l-asparaginase activity when soil is incubated with buffered (0.1 M THAM, pH 10) l-asparagine solution and toluene at 30°C for 2 h. The procedure developed gives quantitative recovery of NH _inf4 ^sup+ -N added to soils and does not cause chemical hydrolysis of l-asparagine. The optimum buffer pH for NH _inf4 ^sup+ -N released by l-asparaginase activity in soils was 10. This enzyme was saturated with 50 mM l-asparagine, and the reaction rate essentially followed zero-order kinetics. The d-isomer of asparagine was also hydrolyzed in soils, but at only 16% of the activity of the l-isomer at a saturating concentration of the substrate. The optimal temperature for the soil l-asparaginase reaction occurred at 60°C and denaturation began at 65°C. The Arrhenius equation plot for l-asparaginase activity in three selected soils was linear between 10 and 50°C. The activation energy values of this enzyme ranged from 20.2 to 34.1 (average 26.6) kJ mol^-1. Application of three linear transformations of the Michaelis-Menten equation showed that the K _m values of l-asparaginase in nine soils ranged from 2.6 to 10.0 (average 6.1) mM and the V _max values ranged from 9 to 131 g NH _inf4 ^sup+ -N released g^-1 soil 2 h^-1. The temperature coefficients (Q ₁₀) for soil l-asparaginase activity ranged from 1.12 to 1.70 (average 1.39). Steam sterilization (121°C for 1 h), formaldehyde, and NaF decreased the activity but the presence of toluene increased the amount of NH _inf4 ^sup+ released. Treatment of soils with dimethylsulfoxide completely destroyed l-asparaginase activity. The use of sulfhydryl reagents indicated that a free sulfhydryl moiety was required to maintain the active enzyme. l-Asparaginase activity in soils was increased by 13 to 18% in the presence of THAM buffer prepared to contain 5 mM Ca²⁺ and Mg²⁺, respectively.     

Three-dimensional deformation measured in an alaskan glacier

Measurements of movement along 28 boreholes reveal the three-dimensional flow field in a 6 million cubic meter reach of Worthington Glacier, a temperate valley glacier located in Alaska. Sliding at the bed accounted for 60 to 70 percent of the glacier's surface motion. Strain rates in the ice were low from the surface to a depth of about 120 meters, but then increased rapidly toward the bed. Ice deformation was not affected by temporal changes in the sliding rate. The three-dimensional pattern of motion indicates that plane strain, which is often assumed by models, is a poor approximation of this viscous flow.     

Echocardiographic evaluation of the effects of medetomidine and xylazine in dogs

The echocardiographic effects of medetomidine and xylazine were evaluated in 6 healthy dogs. Values for echocardiographic variables were significantly different from pre-treatment values after administration of both drugs. The effects of medetomidine were similar to that of xylazine. Because of their cardiac depressant effects, both drugs should be used with care in sick dogs.     

Microscopic Particle Motions in Strongly Coupled Dusty Plasmas

The microscopic particle motions from the crystal to the disordered state of a dusty plasma with micrometer-sized silicon dioxide particle suspensions in a radio-frequency glow discharge system were studied through an optical microimaging system. Small-amplitude random motion around the lattice sites of the crystal state, relative domain motion with varying boundaries, cooperative hopping in the liquid state, and highly disordered motion with increasing radio-frequency power were observed. Chaotic states with different spatial scales under the coherent and stochastic coupling between dust particles and self-organized background plasma fluctuations were also demonstrated.