title: The effects of various anions and cations on the regulation of pyruvate dehydrogenase complex activity from pig kidney cortex.
abstract: The activity of pyruvate dehydrogenase complex (PDC) purified from pig kidney cortex was found to be affected by various uni- and bi-valent ions. At a constant strength of 0.13 M at pH 7.8, K+, Na+, Cl-, HCO3- and HPO4(2-) had significant effects on the activity of PDC: Na+, K+ and HPO4(2-) stimulated, but HCO3- and Cl- inhibited. The stimulatory effect of Na+ was mediated by a change in the Vmax. of PDC only, whereas K+ produced an increase in Vmax. and a change in the Hill coefficient (h). The extent of stimulation produced by HPO4(2-)4 on the activity of PDC was dependent on the concentrations of K+ and Na+. Both cations at concentrations higher than 40 mM partially prevented the effect of HPO4(2-)4. Cl- and HCO3- anions decreased the Vmax. of the enzyme and increased the S0.5 for pyruvate. The effects of Na+, K+, Cl-, HPO4(2-) and HCO3- on the activity of PDC were additive. In the presence of 80 mM-K+, 20 mM-Na+, 10 mM-HPO4(2-), 20 mM-Cl- and 20 mM-HCO3- the activity of PDC was increased by 30%, the S0.5 for pyruvate was increased from 75 to 158 microM and h was decreased from 1.3 to 1.1. Under these conditions and at 1.0 mM-pyruvate, the activity of PDC was 80% of the maximal activity achieved in the presence of these ions and 4.5 mM-pyruvate. The present study suggests that PDC may operate under non-saturating concentrations for substrate in vivo.
authors.affiliation: Department of Biochemistry, University of Texas Health Science Center, San Antonio 78284-7760.
authors.forename: T
authors.initials: T
authors.lastname: Pawelczyk
authors.forename: R A
authors.initials: RA
authors.lastname: Easom
authors.forename: M S
authors.initials: MS
authors.lastname: Olson
mesh_terms: D000818:Animals; D000838:Anions / Q000494:pharmacology*; D001639:Bicarbonates / Q000494:pharmacology; D002414:Cations, Monovalent / Q000494:pharmacology*; D002712:Chlorides / Q000494:pharmacology; D004357:Drug Synergism; D066298:In Vitro Techniques; D007672:Kidney Cortex / Q000187:drug effects / Q000201:enzymology*; D010710:Phosphates / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011768:Pyruvate Dehydrogenase Complex / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology; D013552:Swine
chemical_list: D000838:Anions; D001639:Bicarbonates; D002414:Cations, Monovalent; D002712:Chlorides; D010710:Phosphates; D011768:Pyruvate Dehydrogenase Complex; D012964:Sodium; D011188:Potassium