SPATIAL HETEROGENEITY OF SUBSTRATES: EFFECTS ON HYDROLYSIS, IMMOBILIZATION AND NITRIFICATION OF UREA-N

1986 ◽  
Vol 66 (3) ◽  
pp. 499-511 ◽  
Author(s):  
C. MONREAL ◽  
W. B. McGILL ◽  
M. NYBORG
Keyword(s):  
Maximum Velocity ◽  
Kinetic Studies ◽  
Soil Samples ◽  
Urea Hydrolysis ◽  
N Transformations ◽  
Nest Placement ◽  
Km Value ◽  
Rate Of Hydrolysis ◽  
High Concentrations ◽  
Menten Constant

Hydrolysis, immobilization and nitrification of urea-N was measured in samples of Ap horizons of a Black Chernozemic and a Luvisolic soil incubated in the laboratory. Urea was either placed as a nest or mixed throughout the soil. Samples were removed over time to determine the two-dimensional redistribution of urea, [Formula: see text], [Formula: see text], and [Formula: see text]. Localizing urea in a nest reduced both its rate of hydrolysis and subsequent nitrification, and increased recovery of added N in the presence of straw equivalent to 4 t ha−1. In contrast, urea mixed into the soil was nearly completely hydrolyzed and oxidized in 8 d or completely immobilized in the presence of straw. Kinetic studies showed urea hydrolysis was inhibited in a Luvisolic soil sample with increasing substrate concentration beyond 5 mM. The apparent Michaelis-Menten constant (Ka) was 19 mM; the inhibition constant (Ki) was 7 mM; and apparent maximum velocity (Va) was 34.5 μg N g−1 h−1. Urease activity in the Black Chernozemic soil was described by normal Michaelis-Menten kinetics with a Km value of 3.4 mM and Vmax equal to 18.2 μg N g−1 h−1. When urea was localized in a nest, most of the nitrite oxidizers originally present in the soil were killed during the first 24 d of incubation. Factors such as solubilized organics, in addition to [Formula: see text] and [Formula: see text] were considered to be involved. It was concluded that nest placement of urea influenced N transformations in two ways. First, the low surface area:mass ratio reduced exposure of urea to the soil, thereby slowing processes such as immobilization by organisms on decomposing straw. Second, at the microsite level, high concentrations of urea can inhibit urease; and NH3, once generated in such concentrated localized areas, can itself inhibit nitrification through direct toxic effects or possibly through dissolution of inhibitory organics. Key words: Kinetics, Michaelis-Menten, inhibition, nest placement, nitrification, urea

Inhibitory effect of soil humic compounds on the proteolytic enzyme pronase

Soil Research ◽  
1969 ◽  
Vol 7 (3) ◽  
pp. 241
Author(s):  
JN Ladd ◽  
JHA Butler
Keyword(s):  
Humic Acids ◽  
Maximum Velocity ◽  
Kinetic Studies ◽  
Inhibitory Effect ◽  
Enzymic Activity ◽  
Humic Compounds ◽  
Km Value ◽  
Group Basis ◽  
Inhibitory Power ◽  
Hydrolysis Of

Neutralized solutions of soil humic acids inhibit the proteolytic activity of the enzyme pronase when tested against a variety of substrates. Protein hydrolysis was less sensitive than hydrolysis of dipeptide derivatives; 50% inhibition of benzyloxycarbonylglycylleucine hydrolysis was achieved with concentrations of humic acids as low as 1-2 �g/ml or less than 10-5M, on a carboxyl group basis. Humic acids, extracted from soils with different crop histories, showed only slight differences in their effectiveness as inhibitors of pronase activity. Their inhibitory power was comparable with that of other high molecular weight polyanions, e.g. polyacrylic acid and polycondensates derived from p-benzoquinone and catechol. Alginic acid was a relatively poor inhibitor. Preincubation of humic acids for various periods with either pronase or substrate (albumin or benzyloxycarbonylglycylleucine) had little or no effect on the subsequent inhibition of enzymic activity. However, inhibition is decreased by increasing substrate concentrations, following preincubation of humic acids and pronase. Both observations are consistent with a reversible inhibitory mechanism. Kinetic studies demonstrate that humic acids inhibit pronase activity towards albumin and N-benzyloxycarbonyl dipeptides by effectively reducing the affinity of pronase for the substrate, i.e. by increasing the Km value for the reaction. With benzoylarginine amide and benzoylarginine ethyl ester as substrates, the reaction velocity is lowered due to a reduction of the maximum velocity of the system. Both effects may possibly be explained by a conformational change in the enzyme structure due to combination with the humic acid molecules.

scholarly journals Partial Purification and Characterization of Catalase from Banana Peels

2016 ◽  
Vol 13 (2) ◽  
pp. 392-398
Author(s):  
Baghdad Science Journal
Keyword(s):  
Gel Filtration ◽  
Maximum Velocity ◽  
Kinetic Studies ◽  
Maximal Activity ◽  
Partial Purification ◽  
Purification And Characterization ◽  
Km Value ◽  
Almost All ◽  
Kinetics Of

Catalase (EC 1.11.1.6) is a well known enzyme which exists in almost all living creatures exposing to oxygen (such as plants, bacteria, and animals). It is a very necessary enzyme to protect the cell from oxidative detriment by reactive oxygen species (ROS). The aim of this study is the partial purification and characterization of Catalase enzyme from Banana peels. In this study, fresh banana peels are treated with 70 % ethanol ,further separated with chloroform ,water and ethyl acetate respectively .The supernatant of the enzymatic sample which is treated with chloroform is loaded into gel filtration column with Sephadex G-100 (1.0 x 90 cm) equilibrated with pH7 buffer media (phosphate buffer 0.1 M). Kinetic studies of the purified enzyme activity are measured and characterized .The maximal activity (26.04 units/mg) of catalase is observed with chloroform buffer extraction. The kinetics of catalase; Michalis constant Km and maximum velocity Vmax is determined using Linweaver- Burk plot, The Km value for catalase (434.7mM), Vmax (100 m mole min -1). Characterization results demonstrate that the optimal pH for activity is (7.6). And the optimal temperature for activity is 30?C .The present study indicates that Banana peels is a good source of catalase enzyme.

Corrigenda - Inhibitory effect of soil humic compounds on the proteolytic enzyme pronase

Soil Research ◽  
1969 ◽  
Vol 7 (3) ◽  
pp. 241
Author(s):  
JN Ladd ◽  
JHA Butler
Keyword(s):  
Humic Acids ◽  
Maximum Velocity ◽  
Kinetic Studies ◽  
Inhibitory Effect ◽  
Enzymic Activity ◽  
Humic Compounds ◽  
Km Value ◽  
Group Basis ◽  
Inhibitory Power ◽  
Hydrolysis Of

Neutralized solutions of soil humic acids inhibit the proteolytic activity of the enzyme pronase when tested against a variety of substrates. Protein hydrolysis was less sensitive than hydrolysis of dipeptide derivatives; 50% inhibition of benzyloxycarbonylglycylleucine hydrolysis was achieved with concentrations of humic acids as low as 1-2 �g/ml or less than 10-5M, on a carboxyl group basis. Humic acids, extracted from soils with different crop histories, showed only slight differences in their effectiveness as inhibitors of pronase activity. Their inhibitory power was comparable with that of other high molecular weight polyanions, e.g. polyacrylic acid and polycondensates derived from p-benzoquinone and catechol. Alginic acid was a relatively poor inhibitor. Preincubation of humic acids for various periods with either pronase or substrate (albumin or benzyloxycarbonylglycylleucine) had little or no effect on the subsequent inhibition of enzymic activity. However, inhibition is decreased by increasing substrate concentrations, following preincubation of humic acids and pronase. Both observations are consistent with a reversible inhibitory mechanism. Kinetic studies demonstrate that humic acids inhibit pronase activity towards albumin and N-benzyloxycarbonyl dipeptides by effectively reducing the affinity of pronase for the substrate, i.e. by increasing the Km value for the reaction. With benzoylarginine amide and benzoylarginine ethyl ester as substrates, the reaction velocity is lowered due to a reduction of the maximum velocity of the system. Both effects may possibly be explained by a conformational change in the enzyme structure due to combination with the humic acid molecules.

In-vitro conversion of thyroxine to tri-iodothyronine by chicken hepatic 5′-deiodinase: kinetic studies

1986 ◽  
Vol 110 (3) ◽  
pp. 441-446 ◽  
Author(s):  
S. K. Lam ◽  
S. Harvey
Keyword(s):  
Tissue Concentration ◽  
Maximum Velocity ◽  
Kinetic Studies ◽  
Enzymatic System ◽  
Concentration Time ◽  
Liver Homogenates ◽  
Kinetics Of ◽  
Menten Constant

ABSTRACT In-vitro studies with chicken liver homogenates demonstrate that the conversion of thyroxine (T4) to tri-iodothyronine (T3) is dependent upon tissue concentration, time of incubation, pH, temperature, the presence of dithiothreitol (DTT) and the concentration of substrate (T4), and is heat-labile. The generation of T3 is inhibited by iopanoic acid and 6-n-propyl-2-thiouracil. The kinetics of conversion of T4 to T3, determined by Lineweaver–Burke analysis, indicated an apparent Michaelis–Menten constant (Km) of 1·16 μmol/l with a maximum velocity (Vmax) of 44·57 pmol T3 generated/mg protein per min from T4. Dithiothreitol appears to behave as a co-substrate for this system with an apparent Km of 98·5 μmol/l and a Vmax of 1·41 pmol T3 generated/mg protein per min at a T4 concentration of 5 μmol/l. These data suggest that the conversion of T4 to T3 in fowl proceeds by means of an enzymatic system, probably 5′-monodeiodinase, and is responsible for maintaining T3 levels in vivo. J. Endocr. (1986) 110, 441–446.

In Vitro Diabetogenic Effect of Cadmium on Liver

2017 ◽  
Vol 8 (01) ◽  
Author(s):  
Agung Biworo ◽  
Dwi Rezki Amalia ◽  
Gratianus Billy Himawan ◽  
Lisda Rizky Amalia ◽  
Valentina Halim ◽  
...  
Keyword(s):  
Glucose Metabolism ◽  
Liver Homogenate ◽  
Liver Cells ◽  
Male Rats ◽  
Glycogen Level ◽  
Liver Sample ◽  
Km Value ◽  
Cd Exposure ◽  
Menten Constant

The objectives of this study were to determine the effect of cadmium (Cd) on glucose metabolism disruption in liver cells homogenate in vitro. The glucose metabolism disruption was analyzed by measuring the level of liver glucose, glycogen and methylglyoxal (MG), and the activity of glucokinase activity. In this experiment, a liver sample was taken from male rats (Rattus novergicus). Samples then homogenized and divided into four groups with; C served as control which contains liver homogenate only; T1 which contains liver homogenate + 0.03 mg/l of cadmium sulphate (CdSO4); T2 which contains liver homogenate + 0.3 mg/l of CdSO4; and T3 which contains liver homogenate + 3 mg/l of CdSO4. After treatment, liver glucose, glycogen, and MG levels, and glucokinase activity were estimated. The activity of liver glucokinase was estimated by measuring the Michaelis-Menten constant (Km) value. The results revealed that Cd exposure could significantly increase glucose and MG levels, the Km value of glucokinase, and decreased the glycogen level in liver cells (P>0.05). These results indicated that Cd exposure induced the disruption of glucose metabolism in the liver.

Efficient Preconcentration of Cu2+, Zn2+ and Fe3+ with an Agarose-Schiff Base Sorbent

2007 ◽  
Vol 72 (7) ◽  
pp. 908-916 ◽  
Author(s):  
Payman Hashemi ◽  
Hatam Hassanvand ◽  
Hossain Naeimi
Keyword(s):  
Schiff Base ◽  
Metal Ions ◽  
Metal Ion ◽  
Good Accuracy ◽  
Kinetic Studies ◽  
Sample Volume ◽  
Effects Of Ph ◽  
Glass Column ◽  
High Concentrations ◽  
Ph Range

Sorption and preconcentration of Cu2+, Zn2+ and Fe3+ on a salen-type Schiff base, 2,2'- [ethane-1,2-diylbis(nitrilomethylidyne)]bis(2-methylphenol), chemically immobilized on a highly crosslinked agarose support, were studied. Kinetic studies showed higher sorption rates of Cu2+ and Fe3+ in comparison with Zn2+. Half-times (t1/2) of 31, 106 and 58 s were obtained for sorption of Cu2+, Zn2+ and Fe3+ by the sorbent, respectively. Effects of pH, eluent concentration and volume, ionic strength, buffer concentration, sample volume and interferences on the recovery of the metal ions were investigated. A 5-ml portion of 0.4 M HCl solution was sufficient for quantitative elution of the metal ions from 0.5 ml of the sorbent packed in a 6.5 mm i.d. glass column. Quantitative recoveries were obtained in a pH range 5.5-6.5 for all the analytes. The volumes to be concentrated exceeding 500 ml, ionic strengths as high as 0.5 mol l-1, and acetate buffer concentrations up to 0.3 mol l-1 for Zn2+ and 0.4 mol l-1 for Cu2+ and Fe3+ did not have any significant effect on the recoveries. The system tolerated relatively high concentrations of diverse ions. Preconcentration factors up to 100 and detection limits of 0.31, 0.16 and 1.73 μg l-1 were obtained for Cu2+, Zn2+ and Fe3+, respectively, for their determination by a flame AAS instrument. The method was successfully applied to the metal ion determinations in several river water samples with good accuracy.

scholarly journals Kinetics of Enzymatic Hydrolysis of Southeast Sulawesi Sago Starch

2020 ◽  
pp. 53-61
Author(s):  
Ansharullah Ansharullah ◽  
Muhammad Natsir
Keyword(s):  
Enzymatic Hydrolysis ◽  
Maximum Velocity ◽  
Enzyme Concentration ◽  
Hydrolysis Rate ◽  
Sago Starch ◽  
Optimum Conditions ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Substrate Concentrations ◽  
Menten Constant

The aims of this study were to characterize the kinetics of enzymatic hydrolysis of sago starch, obtained from Southeast Sulawesi Indonesia. The enzyme used for hydrolysis was bacterial ∝-amylase (Termamyl 120L from Bacillus licheniformis, E. C. 3.2.1.1).  The method to determine the initial velocity (Vo) of the hydrolysis was developed by differentiation a nonlinear equation (NLE).  The Vo of the hydrolysis was measured at various pH (6.0, 6.5,and 7.0), temperatures (40, 60, 75 and 95oC), enzyme concentrations (0.5, 1.0, 1.5 and 2.0 µg per mL) and in the presence of 70 ppm Ca++. The optimum conditions of this experiment were found to be at pH 6.5 – 7.0 and 75oC, and the Vo increased with increasing enzyme concentration. The Vo values at various substrate concentrations were also determined, which were then used to calculate the enzymes kinetics constant of the hydrolysis, including Michaelis-Menten constant (Km) and maximum velocity (Vmax) using a Hanes plot.  Km and Vmax values were found to be higher in the measurement at pH 7.0 and 75oC. The Km values  at four  different combinations of pH and temperatures (pH 6.5, 40oC; pH 6.5, 75oC; pH 7.0, 40oC; pH 7.0, 75oC) were found to be 0.86, 3.23, 0.77 and 3.83 mg/mL, respectively; and Vmax values were 17.5, 54.3, 20.3 and 57.1 µg/mL/min, respectively. The results obtained showed that hydrolysis rate of this starch was somewhat low.

scholarly journals The potentional of plants to cleanup metals from an old landfill site

2017 ◽  
Author(s):  
Yahya Jani ◽  
Charlotte Marchand ◽  
William Hogland
Keyword(s):  
Contaminated Soils ◽  
Hazardous Materials ◽  
Average Concentration ◽  
Soil Samples ◽  
Landfill Site ◽  
Group Company ◽  
Timothy Grass ◽  
Xrf Scanning ◽  
High Concentrations ◽  
The Stability

Old landfill sites contain different hazardous materials like heavy metals which have the ability to affects the entire environment. These places are sometimes covered by plants to increase the stability of the soil and to reduce the effects of erosion. 15 soil samples (3 samples from each place) and 5-7 timothy-grass (Phleum pretense) plants from 5 different places were taken from an old landfill place in an active landfill site in Högbytorp /Sweden owned by Ragn-sells Group Company. XRF scanning was used to analyze the metal content of soil samples and of plants. High concentrations of metals were detected in the soil samples like Fe with an average of about 25000 ppm, Mn about 250 ppm and 2800 ppm of Ti. The plants results showed an average concentration of Fe in the shoots about 730 ppm, Mn about 60 ppm and Ti about 1760 ppm. On the other hand, the roots results showed an average concentration of about 10 000 ppm of Fe, about 160 ppm of Mn and 2200 ppm of Ti. These results gave the indication that the Timothy-grass has the ability to extract metals from contaminated soils and can help to cleanup these soils.

scholarly journals The enzymology of short-chain fatty acyl-coenzyme A synthetase from seeds of Pinus radiata. Kinetic studies and a proposed reaction mechanism

1974 ◽  
Vol 137 (3) ◽  
pp. 435-442 ◽  
Author(s):  
Owen A. Young ◽  
John W. Anderson
Keyword(s):  
Fatty Acid ◽  
Pinus Radiata ◽  
Kinetic Studies ◽  
Single Species ◽  
Competitive Inhibitor ◽  
Fatty Acyl ◽  
Short Chain ◽  
Low Concentrations ◽  
High Concentrations ◽  
Acyl Coenzyme A

1. Short-chain fatty acyl-CoA synthetase from seeds of Pinus radiata was examined by acetate- and propionate-dependent PPi–ATP exchange. Reaction mixtures came to equilibrium almost instantly as judged by rates of exchange and analysis of an incubation mixture. 2. The activity of the enzyme was correlated with the concentration of MgP2O72- but not with the concentration of Mg2+, as judged by PPi–ATP exchange and fatty acyl AMP-dependent synthesis of ATP in the presence of PPi. In PPi–ATP exchange assays, no clear relationship between activity and any single species of ATP was apparent. 3. High concentrations of fatty acid inhibited PPi–ATP exchange. PPi–dATP exchange was less than PPi–ATP exchange at low concentrations of fatty acid, but at higher concentrations PPi–dATP exchange exceeded PPi–ATP exchange. The rate of synthesis of fatty acyl-CoA in the presence of dATP was less than with ATP. 4. ATP and propionate inhibited the synthesis of ATP from propionyl-AMP and PPi. The inhibition by ATP was competitive with respect to propionyl-AMP and non-competitive with respect to PPi. The inhibition by propionate was non-competitive with respect to propionyl-AMP and PPi. 5. AMP was a competitive inhibitor of propionyl-AMP-dependent synthesis of ATP and competitively inhibited propionate-dependent PPi–ATP exchange when ATP was the variable substrate. 6. It was concluded that the first partial reaction catalysed by the enzyme is ordered; ATP is the first substrate to react with the enzyme and PPi is probably the only product released.

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