Kinetic Characterization of Mitochondrial Malate Dehydrogenase from Dictyostelium discoideum

Abstract

Malate dehydrogenase (MDH; EC 1.1.1.37) from Dictyostelium discoideum was purified and characterized MDH activity from whole cells was purified 275-fold. The mitochondrial and cytoplasmic MDH present co-purified through three ion exchange and affinity chromatography steps. The isoenzymes were barely separable by either disc gel electrophoresis or isoelectric focusing. The purified preparation containing both isoenzymes had a single pH optimum (9.3-9.5) and an apparent molecular weight of 70000. It exhibited linear kinetics and responded to known inhibitors of MDH, i.e. thyroxine and hydroxymalonate. Michaelis and dissociation constants obtained with this preparation were similar to those obtained with a 10-fold purified mitochondrial MDH.

An Integrated Model of Cardiac Mitochondrial Energy Metabolism and Calcium Dynamics

“…The maximum rate for ADPi:ADPm exchange in the absence of ATP is given by V maxANT . Dudycha et al, 2000;b, Albe et al, 1990;c, calculated from Jeffrey et al, 1999;d, Corkey et al, 1986;e, Singer, 1966;f, adjusted;g, Magnus and Keizer, 1997;h, Magnus, 1995;i, Crompton, 1999; j, calculated from data of Emyanitoff and Kelly, 1982;k, Jung et al, 1989;l, Gunter and Pfeiffer, 1990;m, Wojtczak et al, 1986. The H 1 leakage is considered to be a linear function of the Dm H through a proportionality constant given by the H 1 conductance, g H . Although the actual relationship is roughly exponential (Brown and Brand, 1986) there is an extensive linear region, especially at high DC m values, which justifies simplification of the rate equation, described as follows:…”