Microheterogeneity of the malate dehydrogenase from several sources

Mitochondrial malate dehydrogenase from the thermophilic, filamentous fungus Talaromyces emersonii

Mitochondrial malate dehydrogenase (m-MDH; EC 1.1.1.37), from mycelial extracts of the thermophilic, aerobic fungus Talaromyces emersonii, was purified to homogeneity by sequential hydrophobic interaction and biospecific affinity chromatography steps. Native m-MDH was a dimer with an apparent monomer mass of 35 kDa and was most active at pH 7.5 and 52 degrees C in the oxaloacetate reductase direction. Substrate specificity and kinetic studies demonstrated the strict specificity of this enzyme, and its closer similarity to vertebrate m-MDHs than homologs from invertebrate or mesophilic fungal sources. The full-length m-MDH gene and its corresponding cDNA were cloned using degenerate primers derived from the N-terminal amino acid sequence of the native protein and multiple sequence alignments from conserved regions of other m-MDH genes. The m-MDH gene is the first oxidoreductase gene cloned from T. emersonii and is the first full-length m-MDH gene isolated from a filamentous fungal species and a thermophilic eukaryote. Recombinant m-MDH was expressed in Escherichia coli, as a His-tagged protein and was purified to apparent homogeneity by metal chelate chromatography on an Ni2+-nitrilotriacetic acid matrix, at a yield of 250 mg pure protein per liter of culture. The recombinant enzyme behaved as a dimer under nondenaturing conditions. Expression of the recombinant protein was confirmed by Western blot analysis using an antibody against the His-tag. Thermal stability studies were performed with the recombinant protein to investigate if results were consistent with those obtained for the native enzyme.

Concomitant purification and characterization of malate dehydrogenase, aspartate transaminase, nucleoside diphosphate kinase and enolase from rabbit liver cytosol

A procedure was developed for purifying the cytosolic isoforms of malate dehydrogenase, aspartate transaminase, enolase and nucleoside diphosphate kinase from a single preparation of rabbit liver. The procedure includes chromatography on reactive-dye, radial-flow columns, and elution of enzymes from columns by substrates, to obtain high yields in a minimal amount of time. The scheme avoids steps used in previous methods that are either difficult to execute in large-scale preparations, or alter the native forms of the enzymes. Examination of the purified enzymes by SDS-PAGE indicated that nearly homogeneous preparations had been obtained. The native molecular weight, subunit molecular weight, and isoelectric point(s) were determined for each enzyme. Although preparations of nucleoside diphosphate kinase purified from cytosol showed only a single band on SDS-PAGE, isoelectric focusing revealed the presence of multiple isoforms.

Horse-liver glutathione reductase: purification and characterization

1. Purification of horse-liver glutathione reductase was obtained by affinity chromatography on N6-(6-aminohexyl)-adenosine-1'5'-bisphosphate Sepharose (N6-2'5'-ADP-Sepharose) and Reactive Red-120-Agarose, and chromatography on DEAE-Sephadex and Sephacryl S-300. 2. The final preparation had 248 U/mg specific activity after 11,174-fold purification with 47% final recovery, and was homogeneous by SDS-electrophoresis. It showed charge heterogeneity in non-denaturing electrophoresis and chromatofocusing, with several peaks of pI between 5.7 and 6.7. 3. The enzyme was homodimeric (107,000 native MW), with S20w = 6.31 S, and 41.22 A of hydrodynamic radius. It showed absorption peaks at 270, 370 and 462 nm, a characteristic of flavoproteins. 4. When NADPH was substituted by deamino-NADPH or NADH the enzyme showed 69 and 8.5% activity, respectively, while with glutathione-CoA mixed disulfide the enzyme had 23% of the activity shown with GSSG. Apparent Km values of 8.8, 680, 59, and 560 microM were measured for NADPH, NADH, GSSG and ferricyanide, respectively.

Multiple levels in the control of rhythms in enzyme synthesis and activity by circadian clocks: recent trends

It is now well established that circadian clocks can control rhythmicity at different stages of the sequence of events leading from gene activity to a functional enzyme molecule. Conceptual and experimental distinction of the effective control targets is emphasized, with particular attention to recent results obtained on circadian clock control of transcription and to data indicating that proteins can behave as conformational oscillators. Thus circadian rhythmicity both in gene expression and in the dynamics of the enzyme molecule would contribute to the temporal compartmentation of processes such as metabolic co-ordination and channeling necessary for the adaptive efficiency of physiological programmes.