scholarly journals Saturation kinetics of magnesium efflux across the rumen wall in heifers

1983 ◽  
Vol 49 (1) ◽  
pp. 153-158 ◽  
Author(s):  
H. Martens
Keyword(s):  
Active Process ◽  
Saturation Kinetics ◽  
Kinetics Of ◽  
Menten Constant

1. Absorption of magnesium from the temporarily-isolated, emptied and washed rumen of four 10–12-month-old heifers was measured at five different Mg concentrations (2·5, 5·0, 7·5, 12·5 and 20 mmol/l).2. Net absorption of Mg was observed at all concentrations. Saturation occurred at a concentration of 12·5 mmol Mg/l.3. Using an Eadie–Hofstee plot, the Michaelis–Menten constant (Km; 11·43 mmol/l) and maximal efflux (Vmax; 120·3 μmol/min) were estimated.4. The phenomenon of saturation supports the assumption that Mg transport across the rumen wall of heifers is an active process.

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.

Kinetics of hepatic alanine uptake and urea synthesis in pigs

1988 ◽  
Vol 254 (4) ◽  
pp. G602-G609
Author(s):  
H. Vilstrup ◽  
L. T. Skovgaard
Keyword(s):  
Maximum Rate ◽  
Maximum Likelihood Method ◽  
Blood Flow Rate ◽  
Likelihood Method ◽  
Synthesis Rate ◽  
Urea Synthesis ◽  
Half Maximum ◽  
Concentration Gradients ◽  
Saturation Kinetics ◽  
Kinetics Of

The kinetics of hepatic alanine uptake and urea synthesis in relation to sinusoid alanine concentration was investigated in seven anesthetized pigs weighing 63 kg, using liver vein catheterizations. Each experiment consists of four steady-state periods of 40 min with alanine concentrations in the range of 0.4-27 mmol/l. The process rates were measured as the products of transhepatic concentration gradients and hepatic blood flow rate, determined by indocyanine green. The data suggest that both processes follow saturation kinetics, that there exists a sinusoidal concentration of alanine below which net removal is limited, and that urea synthesis consists of two components: one alanine independent and one depending on alanine concentration according to Michaelis-Menten kinetics. The kinetic parameters were estimated iteratively by the maximum likelihood method. The maximum rate of alanine uptake was 1.13 +/- 0.74 mmol.min-1.kg liver wt-1 (mean +/- SD), the alanine concentration resulting in half-maximum alanine uptake rate was 1.69 +/- 0.99 mmol/l, and the removal-limiting alanine concentration was 0.27 +/- 0.09 mmol/l. The maximum rate of urea-N synthesis was 1.49 +/- 0.87 mmol.min-1.kg liver wt-1, the alanine concentration resulting in half-maximum urea-N synthesis rate was 2.32 +/- 1.11 mmol/l, and the alanine concentration-independent urea-N synthesis rate was 0.13 +/- 0.10 mmol.min-1.kg liver wt-1.

Kinetics of potassium uptake in red spruce seedlings

1985 ◽  
Vol 63 (3) ◽  
pp. 512-516
Author(s):  
J. R. Cumming ◽  
R. T. Eckert ◽  
L. S. Evans
Keyword(s):  
Nonlinear Least Squares ◽  
Theoretical Models ◽  
Potassium Uptake ◽  
Red Spruce ◽  
Saturation Kinetics ◽  
Potassium Absorption ◽  
Parameter Values ◽  
Kinetics Of ◽  
Diffusive Component ◽  
Nutrient Solutions

Potassium uptake by roots of 3-week-old red spruce (Picea rubens Sarg.) seedlings was measured in nutrient solutions ranging in K+ concentration from 0.01 to 10.0 mM. Nonlinear least squares analysis was used to estimate uptake parameters Vmax and Km. Analyses of residuals generated by several theoretical models of ion uptake were undertaken to choose the best mechanistic uptake model. Potassium absorption by red spruce seedlings was characterized by Michaelis–Menten behavior from K+ solutions in the range 0.01 to 1.0 mM. Above 1.0 mM, accumulation of potassium was most readily accounted for by a linear diffusive component superimposed on saturation kinetics. Uptake parameter values of Vmax = 1.17 μmol K∙g fresh weight−1∙h−1 and Km = 0.083 mM were similar to those reported for other species. The culture of seedlings in full-strength nutrient solution did not reduce the ability to resolve these uptake parameters in short-term experiments.

Increasing magnesium intakes in relation to magnesium absorption in dry cows

2004 ◽  
Vol 71 (3) ◽  
pp. 297-303 ◽  
Author(s):  
Surasak Jittakhot ◽  
J Thomas Schonewille ◽  
Hugo Wouterse ◽  
Anton WJ Uijttewaal ◽  
Chalermpon Yuangklang ◽  
...  
Keyword(s):  
Dairy Cow ◽  
Dry Matter ◽  
Rumen Fluid ◽  
Latin Square ◽  
Basal Diet ◽  
Apparent Absorption ◽  
Post Feeding ◽  
Saturation Kinetics ◽  
Kinetics Of

Earlier studies with temporarily isolated rumen of heifers show saturation kinetics of Mg efflux across the rumen wall. Therefore, we hypothesized that high Mg intakes would not further increase the rate of Mg absorption in cows. To test our hypothesis, six ruminally fistulated non-pregnant dry cows were given diets with different Mg concentrations in a 6×6 Latin square design. Desired concentrations of Mg were attained by adding MgO to the basal diet and the Mg concentrations in the total rations were 3·8, 6·4, 9·1, 11·8, 14·1 and 17·3 g Mg/kg dry matter, which provided Mg intakes of 27·1, 44·6, 64·6, 83·5, 100·4 and 124·3 g/d, respectively. Increasing Mg intakes were associated with increased (P<0·001) faecal Mg excretion. However, apparent Mg absorption expressed as g/d was not significantly different for Mg intakes from 100·4 to 124·3 g/d while Mg absorption expressed as a proportion of intake was not significantly different for Mg intakes ranging from 64·6 to 124·3 g/d. Mg concentrations in rumen fluid after feeding increased (P<0·001) with increasing Mg intakes. Apparent absorption of Mg appeared to become saturated at a ruminal Mg concentration of 17·5 mM (Mg intake of 83·5 g/d). Group-mean post-feeding concentrations of Mg and Na in rumen fluid were significantly correlated (Pearson's r=−0·96; P=0·003, n=6). This study showed that under conditions of practical dairy cow feeding, Mg absorption was maximal at Mg intakes [ges ]84 g/d.

Fabricating Necklace-, Tower-, and Rod-Shaped In2O3 Nanostructures by Controlling Saturation Kinetics of Catalyst Droplets in a Vapor–Liquid–Solid Process

2017 ◽  
Vol 17 (9) ◽  
pp. 4596-4602 ◽  
Author(s):  
J. Alberto Ramos Ramón ◽  
Ana Cremades ◽  
David Maestre ◽  
Rutilo Silva González ◽  
Umapada Pal
Keyword(s):  
Vapor Liquid Solid ◽  
Saturation Kinetics ◽  
Kinetics Of ◽  
In2o3 Nanostructures ◽  
Vapor Liquid

Role of the kidney in human leptin metabolism

1997 ◽  
Vol 273 (5) ◽  
pp. E903-E907 ◽  
Author(s):  
Christian Meyer ◽  
Dave Robson ◽  
Noya Rackovsky ◽  
Veena Nadkarni ◽  
John Gerich
Keyword(s):  
Renal Vein ◽  
Human Kidney ◽  
Maximal Velocity ◽  
Substantial Role ◽  
Saturation Kinetics ◽  
Menten Constant

To assess the role of the human kidney in leptin metabolism, we measured renal leptin net balance and urinary leptin excretion in 16 normal postabsorptive volunteers with varying degrees of obesity. Arterial leptin concentrations (11.6 ± 2.7 ng/ml) significantly exceeded renal vein concentrations (10.3 ± 2.5 ng/ml, P < 0.001). Renal leptin fractional extraction averaged 13.1 ± 1.1%, and renal leptin net balance (uptake) averaged 1,070 ± 253 ng/min. Lineweaver-Burk analysis indicated that renal leptin uptake followed saturation kinetics with an apparent Michaelis-Menten constant of 10.9 ng/ml and maximal velocity of 1,730 ng/min. Leptin was generally undetectable in urine. Using literature values for systemic leptin clearance, we calculated that renal leptin uptake could account for ∼80% of all leptin removal from plasma. These data indicate that the human kidney plays a substantial role in leptin removal from plasma by taking up and degrading the peptide.

Saturation kinetics of the S0 to S2 optical transition in isolated diphenylhexatriene

1985 ◽  
Vol 82 (7) ◽  
pp. 2939-2941 ◽  
Author(s):  
Bryan E. Kohler ◽  
Thomas A. Spiglanin
Keyword(s):  
Optical Transition ◽  
Saturation Kinetics ◽  
Kinetics Of
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