title: Effect of pH on the stability of hexokinase and glucose 6-phosphate dehydrogenase.
abstract: Hexokinase (HK) and glucose 6-phosphate dehydrogenase (G6PDH) are important enzymes used in biochemical studies and in analytical methods. The stability of the enzymes can be affected by several variables, pH being one of them. The effect of pH on the stability of HK and G6PDH was evaluated in this work. Baker's yeast cells were suspended in 50 mM Tris-HCl buffer (pH 7.5) containing 5.0 mM MgCl2, and submitted to disruption by agitation with glass beads and in the presence of protease inhibitors. The cell-free extract was obtained by centrifugation (2880g; 10 min), followed by dilution into the buffers: 0.1 M acetate-acetic acid (pH: 4.0, 4.5, 5.0, or 5.5), 0.1 M phosphate buffer (pH: 6.0, 6.5, or 7.0), and 0.1 M Tris-HCl buffer (pH: 7.5, 8.0, 8.5, 9.0 or 9.5). The residual activity of HK and G6PDH, expressed as micromol of NADPH formed per min, were measured through a period of buffer-enzyme contact from 0 to 51 h at 4 degrees C. It was observed that up to 4 h both enzymes were stable in all buffers used. However, after 51 h HK was stable at pH 6.0 and 7.5, whereas G6PDH was stable at pH 7.0, 9.5, and between 4.5 and 5.5.
authors.affiliation: Department of Biochemical and Pharmaceutical Technology, School of Pharmaceutical Sciences, University of São Paulo, SP, Brazil.
authors.forename: Maria Aparecida
authors.initials: MA
authors.lastname: Souza
authors.forename: Marcela Zanella
authors.initials: MZ
authors.lastname: Ribeiro
authors.forename: Daniel Pereira
authors.initials: DP
authors.lastname: Silva
authors.forename: Adalberto
authors.initials: A
authors.lastname: Pessoa
authors.forename: Michele
authors.initials: M
authors.lastname: Vitolo
mesh_terms: D004795:Enzyme Stability; D005954:Glucosephosphate Dehydrogenase / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D006593:Hexokinase / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D013997:Time Factors
chemical_list: D005954:Glucosephosphate Dehydrogenase; D006593:Hexokinase