An enzymatic method for determination of urinary lactate and urinary lactate levels in normal children

Lactate irreversible disposal (RiLa) and oxidation (RoxLa) rates were studied in six male subjects during rest (Re), easy exercise [EE, 140 min of cycling at 50% of maximum O2 consumption (VO2max)] and hard exercise (HE, 65 min at 75% VO2max). Twenty minutes into each condition, subjects received a Na+-L(+)-[1–13C]lactate intravenous bolus injection. Blood was sampled intermittently from the contralateral arm for metabolite levels, acid-base status, and enrichment of 13C in lactate. Expired air was monitored continuously for determination of respiratory parameters, and aliquots were collected for determination of 13C enrichment in CO2. Steady-rate values for O2 consumption (VO2) were 0.33 +/- 0.01, 2.11 +/- 0.03, and 3.10 +/- 0.03 l/min for Re, EE, and HE, respectively. Corresponding values of blood lactate levels were 0.84 +/- 0.01, 1.33 +/- 0.05, and 4.75 +/- 0.28 mM in the three conditions. Blood lactate disposal rates were significantly correlated to VO2 (r = 0.78), averaging 123.4 +/- 20.7, 245.5 +/- 40.3, and 316.2 +/- 53.7 mg X kg-1 X h-1 during Re, EE, and HE, respectively. Lactate oxidation rate was also linearly related to VO2 (r = 0.81), and the percentage of RiLa oxidized increased from 49.3% at rest to 87.0% during exercise. A curvilinear relationship was found between RiLa and blood lactate concentration. It was concluded that, in humans, 1) lactate disposal (turnover) rate is directly related to the metabolic rate, 2) oxidation is the major fate of lactate removal during exercise, and 3) blood lactate concentration is not an accurate indicator of lactate disposal and oxidation.

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Determination of uric acid in human serum by an enzymatic method using N-methyl-N-(4-aminophenyl)-3-methoxyaniline reagent

Journal of the Serbian Chemical Society ◽

10.2298/jsc0309691j ◽

2003 ◽

Vol 68 (8-9) ◽

pp. 691-698 ◽

Cited By ~ 7

Author(s):

Milena Jelikic-Stankov ◽

Predrag Djurdjevic ◽

Dejan Stankov

Keyword(s):

Uric Acid ◽

Human Serum ◽

Limit Of Detection ◽

Ascorbate Oxidase ◽

Acid Oxidation ◽

Uric Acid Concentration ◽

Enzymatic Method ◽

Limit Of Quantification ◽

Relative Standard

In this work a new enzymatic method for the determination of uric acid in human serum has been developed. The method is based on the oxidative coupling reaction between the N-methyl-N-(4-aminophenyl)-3-methoxyaniline (NCP) reagent and the hydrogen ? donor reagent N-ethyl-N-(2-hydroxy-3-sulfopropyl)-3-methylaniline (TOOS), in the system involving three enzymes: uricase, peroxidase and ascorbate oxidase. Using this method uric acid could be determined in concentrations up to 1.428 mmol/L, with a relative standard deviation of up to 1.8 %. The effect of the medium pH and the NCP concentration on the linearity of the chromogen absorbance versus the uric acid concentration curve was investigated. The influence of the uricase activity on the maximum rate of uric acid oxidation was also examined. The use of the NCP reagent demonstrated a more precise and more sensitive determination of the uric acid compared to the determination with 4-aminoantipyrine (4-AA) as the coupling regent. The sensitivity of the method determined from the calibration curve was 0.71 absorbance units per mmol/L of uric acid; the limit of detection was LOD = 0.0035 mmol/L and the limit of quantification was LOQ = 0.015 mmol/L of uric acid.

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Kinetic Enzymatic Method for Determining Serum Creatinine

Clinical Chemistry ◽

10.1093/clinchem/21.10.1422 ◽

1975 ◽

Vol 21 (10) ◽

pp. 1422-1426 ◽

Cited By ~ 54

Author(s):

Gerald A Moss ◽

Richard J L Bondar ◽

Diane M Buzzelli

Keyword(s):

Serum Creatinine ◽

Accurate Determination ◽

Test Subject ◽

Rate Of Change ◽

Enzymatic Method ◽

Inhibitory Effects ◽

Standard Curve ◽

Analytical Recovery ◽

Enzymatic Procedure

Abstract Creatinine amidohydrolase is used to measure serum creatinine in a totally enzymatic procedure. Creatine, produced by hydrolysis, is acted upon by creatine kinase, and then by pyruvate kinase and lactate dehydrogenase, to result in a change in absorbance at 340 nm. The amount of creatinine present is related to the rate of change in A340 and is determined from a standard curve. Absorbance and concentration are linearly related to 100 mg/liter and only 250 µl of serum is required. At 1.0 g/liter, heparin, oxalate, citrate, ethylenediaminetetraacetate, ascorbate, or glucose had no significant effect on the accurate determination of creatinine; higher concentrations (30 g/liter) had inhibitory effects on the test. Analytical recovery of creatinine added to either normal or abnormal sera averaged 102%. When results of this procedure and of the standard direct Jaffé test were compared, the latter were significantly higher. Unlike the Jaffé method, the present method of determining creatinine is rapid (about 10 min per test), subject to few or no interfering substances, and requires no serum deproteinization.

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