title: Preliminary evaluation of an improved enzymatic assay method for measuring potassium concentrations in serum.
abstract: BACKGROUND
  K(+) has important physiological functions. K(+) concentrations in serum are generally determined using ion-selective electrodes (ISEs), though measurement using reagents in aqueous medium is also useful.
  
  
  METHODS
  K(+) concentrations were measured using recombinant inosine 5'-monophosphate dehydrogenase (IMPDH), which was activated only by K(+) and NH4(+). Exogenous NH4(+) and endogenous NH4(+) were eliminated using glutamine synthase.
  
  
  RESULTS
  Regression analysis of the enzymatic assay (y) vs. the ISE method (x) gave the following relation: y=1.03x+0.09 (n=54, Sy,x=0.06 mmol/l). The linear range was up to 12 mmol/l when 1 U/ml IMPDH was used.
  
  
  CONCLUSIONS
  Advantages of the proposed assay method are: (i) the measured range is wider than that of existing enzymatic methods; (ii) the conditions for K(+) determination can be maintained constant, regardless of the amount of NH4(+) in the analyte and reagents; and (iii) the elimination system is simpler because the recombinant IMPDH is stimulated by only K(+) and NH4(+) and is unaffected by biological materials.
authors.affiliation: Division of Biological Science and Technology, Department of Health Science, Faculty of Medical Sciences, Kyushu University, Japan.
authors.forename: Eri
authors.initials: E
authors.lastname: Ota
authors.affiliation: Asahi Kasei Pharma Corporation, Japan. Electronic address: sakasegawa.sb@om.asahi-kasei.co.jp.
authors.forename: Shin-ichi
authors.initials: S
authors.lastname: Sakasegawa
authors.affiliation: Asahi Kasei Pharma Corporation, Japan.
authors.forename: Shigeru
authors.initials: S
authors.lastname: Ueda
authors.affiliation: Asahi Kasei Pharma Corporation, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Konishi
authors.affiliation: Division of Biological Science and Technology, Department of Health Science, Faculty of Medical Sciences, Kyushu University, Japan.
authors.forename: Masaru
authors.initials: M
authors.lastname: Akimoto
authors.affiliation: Division of Biological Science and Technology, Department of Health Science, Faculty of Medical Sciences, Kyushu University, Japan.
authors.forename: Takiko
authors.initials: T
authors.lastname: Tateishi
authors.affiliation: Division of Biological Science and Technology, Department of Health Science, Faculty of Medical Sciences, Kyushu University, Japan.
authors.forename: Miki
authors.initials: M
authors.lastname: Kawano
authors.affiliation: Division of Biological Science and Technology, Department of Health Science, Faculty of Medical Sciences, Kyushu University, Japan.
authors.forename: Eisaku
authors.initials: E
authors.lastname: Hokazono
authors.affiliation: Division of Biological Science and Technology, Department of Health Science, Faculty of Medical Sciences, Kyushu University, Japan.
authors.forename: Yuzo
authors.initials: Y
authors.lastname: Kayamori
mesh_terms: D057075:Enzyme Assays / Q000592:standards*; D006801:Humans; D017736:Ion-Selective Electrodes / Q000592:standards; D011188:Potassium / Q000097:blood*
chemical_list: D011188:Potassium
keywords: Enzymatic assay method; Inosine 5′-monophosphate dehydrogenase; Potassium