Papers by Lorenzo Prencipe
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Enzymic assay of creatinine in serum and urine with creatinine iminohydrolase and glutamate dehydrogenase
Clinical Chemistry, 1982
We describe an assay for creatinine in which it is converted by creatinine iminohydrolase (EC 3.5... more We describe an assay for creatinine in which it is converted by creatinine iminohydrolase (EC 3.5.4.21) into ammonia and N-methylhydantoin. The ammonia is subsequently assayed by use of alpha-ketoglutarate and glutamate dehydrogenase (EC 1.4.1.3). Use of NADPH as coenzyme eliminates all interferences from endogenous reactions. Endogenous ammonia in the sample is eliminated during a preincubation. The reaction reaches the endpoint in 15 min at working temperatures of 20-37 degrees C. No sample blank or reagent blank is needed. The standard curve is linear at least to 884 mumol (100 mg) of creatinine per liter. Average analytical recovery of creatinine in serum and urine is 99%. Within-run and between-run CVs are less than or equal to 2% and less than or equal to 6% for creatinine values of 335 mumol/L (38 mg/L) and 80 mumol/L (0 mg/L), respectively. Results by the described method (y) compare well with those by Jaffé's kinetic test (y = 1.01x -- 12.8), Berthelot/AutoAnalyzer meth...
Clinical Chemistry, 1983
We describe a new colorimetric method for measuring creatinine in serum and urine. Creatinine hyd... more We describe a new colorimetric method for measuring creatinine in serum and urine. Creatinine hydrolysis is catalyzed by creatinine amidohydrolase, and the creatine so produced is assayed in reactions catalyzed sequentially by creatine amidinohydrolase and sarcosine oxidase in a system that generates hydrogen peroxide. The hydrogen peroxide is measured at 510 nm in a reaction catalyzed by horseradish peroxidase, with 3,5-dichloro-2-hydroxybenzenesulfonic acid/4-aminophenazone as the chromogen. This series of reactions is complete in 30 min at room temperature. A blank sample measurement corrects for endogenous creatine. The standard curve is linear for creatinine concentrations as great as 2.21 mmol/L. Analytical recovery of creatinine in human sera and urine averaged 99.8%. Within-run and between-run precision studies gave CVs of less than or equal to 3.3 and less than or equal to 4.3% for a serum with a creatinine concentration of 69 mumol/L. Results by this method agree well (r g...
Clinical Chemistry, 1980
A new direct colorimetric procedure for uric acid assay in serum or urine is described, utilizing... more A new direct colorimetric procedure for uric acid assay in serum or urine is described, utilizing a 3,5-dichloro-2-hydroxybenzene sulfonic acid/4-aminophenazone chromogenic system in the presence of horseradish peroxidase and uricase from Aspergillus flavus. This chromogen system has a high absorptivity, affording useful results with sample/reagent volume ratios as low as 0.025. The procedure is applicable to serum, plasma, or diluted urine. A single working reagent is used; the reaction is complete in less than 15 min at room temperature. The red dye formed is measured at 520 nm; a blank sample measurement is not needed. The standard curve for the method is linear for uric acid concentrations up to 1500 mumol/L. Average analytical recovery of uric acid in human sera and urine exceeded 99%; within-run and between-run precision studies showed CV's of less than or equal to 1.2 and less than or equal to 2.2%, respectively. The new procedure correlated well with the uricase/catalase...
Clinical Chemistry, 1994
We describe an improved enzymatic ultraviolet absorbance method for assaying creatinine in serum,... more We describe an improved enzymatic ultraviolet absorbance method for assaying creatinine in serum, plasma, and urine. Creatinine is hydrolyzed by creatinine iminohydrolase (EC 3.5.4.21) to ammonia and N-methylhydantoin. The ammonia produced combines with 2-oxoglutarate and NADPH in the presence of glutamate dehydrogenase to yield glutamate and NADP+. The consumption of NADPH, measured by a two-point fixed-time assay, is proportional to the amount of creatinine in the sample. The assay is carried out in two steps: The first step eliminates background absorbance in hyperlipemic samples and endogenous ammonia through a "clearing system" and an isocitrate dehydrogenase-based "ammonia scavenger system"; the second step starts creatinine measurement. The method affords a simple, rapid, and sensitive assay with good precision and extended linearity; it employs working solutions stable at least 4 months. Test results compare closely with those of the isotope dilution-mass...
Clinical Chemistry, 2010
Use of 3,5-dichloro-2-hydroxybenzenesulfonic acid/4aminophenazone chromogenic system in direct en... more Use of 3,5-dichloro-2-hydroxybenzenesulfonic acid/4aminophenazone chromogenic system in direct enzymic assay of uric acid in serum and urine. Clin Chem 1980;26:227-31. 3 Our 1980 report in Clinical Chemistry described an improved chromogenic detection system that, coupled with the enzyme oxidation of uric acid, led to a direct method for assaying uric acid in biological fluids. The system assay was reliable, simple, rapid, and suitable for either manual or automated procedures. The work was developed in the context of the Sera-Pak line of clinical chemistry reagents at Miles Italiana SpA's Ames research and development laboratories. This line of reagents was marketed in 58 countries throughout the world. Before our investigation, chemical and enzymatic methods for uric acid assay had been described, but these assays had practical disadvantages: lack of direct assay in a small sample with a single reagent, need for a serum blank, long incubation times, and false negatives or positives due to interfering substances. The oxidation coupling reaction between phenol and 4-aminophenazone to yield red quinoneimine dye had long been known, and the reaction widely used in clinical chemistry since Trinder applied it to the enzymatic determination of glucose (1 ). We speculated that a similar approach might be suitable for measuring uric acid. However, difficulties were encountered, which included the low uric acid concentration in serum and incompatibility between the working pH of horseradish peroxidase and that of animal-originated uricase. Furthermore, the Emerson-Trinder chromogenic system had the major drawback that the oxidative coupling reaction was affected by bilirubin and reducing compounds. This drawback could decrease reaction color as concentrations of these substances increased (2 ). The interference by reducing compounds such as ascorbic acid primarily consists of either competition with the chromogen in the
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Papers by Lorenzo Prencipe