title: Enzymatic determination of potassium in serum.
abstract: This is a kinetic assay for measuring K+ in serum, based on the activation of pyruvate kinase (EC 2.7.1.40) by K+. We eliminated interference from Na+ and NH4+ ions, which also activate this enzyme, by including Na+-binding and NH4+-consuming reagents in the reaction mixture. The assay was developed with and evaluated in the Cobas Fara centrifugal analyzer (and has been used in other kinetic analyzers). Within-run and between-run CVs were less than 1.4% and less than 1.6%, respectively. The reaction rate per millimole of K+ per liter (0.05 delta A/min) was more than double that of the reagent blank (0.02 delta A/min). Results correlated well with those by flame photometry, and interference from bilirubin, hemoglobin, lipids, heparin, and other cations was negligible. This method, in conjunction with a previous method we have reported in which beta-galactosidase is used for measuring Na+ in serum, offers a practical alternative to the use of ion-selective electrodes and flame photometry for measuring these clinically important monovalent cations in high-throughput or "stat" biochemical analyzers.
authors.affiliation: Department of Biochemistry and Chemical Pathology, Flinders University of South Australia, Bedford Park, Australia.
authors.forename: M N
authors.initials: MN
authors.lastname: Berry
authors.forename: R D
authors.initials: RD
authors.lastname: Mazzachi
authors.forename: M
authors.initials: M
authors.lastname: Pejakovic
authors.forename: M J
authors.initials: MJ
authors.lastname: Peake
mesh_terms: D000641:Ammonia; D001322:Autoanalysis / Q000295:instrumentation; D002498:Centrifugation / Q000379:methods; D002614:Chelating Agents; D006801:Humans; D011188:Potassium / Q000097:blood*; D011770:Pyruvate Kinase; D012964:Sodium; D013053:Spectrophotometry
chemical_list: D002614:Chelating Agents; D000641:Ammonia; D012964:Sodium; D011770:Pyruvate Kinase; D011188:Potassium