Rapid purification of yeast alcohol dehydrogenase

Extraction of Proteins and Other Intracellular Bioactive Compounds From Baker's Yeasts by Pulsed Electric Field Treatment

Yeasts are rich source of proteins, antioxidants, vitamins, and other bioactive compounds. The main drawback in their utilization as valuable ingredients in functional foods and dietary supplements production is the thick, indigestible cell wall, as well as the high nucleic acid content. In this study, we evaluated the feasibility of pulsed electric field (PEF) treatment as an alternative method for extraction of proteins and other bioactive intracellular compounds from yeasts. Baker's yeast water suspensions with different concentration (12.5-85 g dry cell weight per liter) were treated with monopolar rectangular pulses using a continuous flow system. The PEF energy required to achieve irreversible electropermeabilization was significantly reduced with the increase of the biomass concentration. Upon incubation of the permeabilized cells in water, only relatively small intracellular compounds were released. Release of 90% of the free amino acids and low molecular UV absorbing compounds, 80% of the glutathione, and ∼40% of the total phenol content was achieved about 2 h after pulsation and incubation of the suspensions at room temperature. At these conditions, the macromolecules (proteins and nucleic acids) were retained largely inside. Efficient protein release (∼90% from the total soluble protein) occurred only after dilution and incubation of the permeabilized cells in buffer with pH 8-9. Protein concentrates obtained by ultrafiltration (10 kDa cut off) had lower nucleic acid content (protein/nucleic acid ratio ∼100/4.5) in comparison with cell lysates obtained by mechanical disintegration. The obtained results allowed to conclude that PEF treatment can be used as an efficient alternative approach for production of yeast extracts with different composition, suitable for application in food, cosmetics and pharmaceutical industries.

Electrically induced protein release from Schizosaccharomyces pombe cells in a hyperosmotic condition during and following a high electropulsation

A high-electric-field application of fission yeast cells under hyperosmotic conditions improved the electro-induced release of protein and cytoplasmic enzymes. A cell suspension was pulsed at 12.5 kV/cm for 10 ms in a batch system and immediately postincubated at 30 degrees C. The total protein release rate from cells increased in the hypertonic solutions of 1.5-2.5 M sorbitol to approximately threefold higher than those in the hypotonic and isotonic solutions of 0-0.5 M sorbitol. The protein release rate in 2.0 M sorbitol greatly increased up to 4.5 h and then gradually increased after 7.5 h. The maximum activities of cytoplasmic enzymes, such as alcohol dehydrogenase and 3-phosphoglycerate kinase, were obtained at 7.5 h after electropulsation in 2.0 M sorbitol, yielding approximately 90% of the enzyme activity levels found in spheroplast lysate. On the other hand, the release rates of protease in vacuoles and invertase in periplasmic space did not depend on osmotic solutions during electric pulse application.

Kinetic properties of native and mutagenized isoforms of mitochondrial alcohol dehydrogenase III purified from Kluyveromyces lactis

By computer modelling and protein engineering we have investigated changes in two amino acid residues located in the coenzyme pocket of the yeast Kluyveromyces lactis mitochondrial alcohol dehydrogenase III. These two residues, Gly 225 and Ala 274, were hypothesized to be involved in the enzyme discrimination between NAD(H) and NADP(H). Upon changing Gly 225 to Ala we produced an enzyme (mutant G225A) showing very little difference from the wild-type. On the contrary, change at position 274 of Phe instead of Ala (mutant A274F) caused a significant increase of K(m) values for NAD(P) and for NADPH and even a more marked decrease in catalytic activity. The k(cat)/K(m) rates for NADP(H) were also decreased in this mutant. Enzymes with the double changes at 225 and 274 (mutant G225A-A274F) showed, apart the substantial low K(m) value for NADPH and its high catalytic efficiency, kinetic parameters relative to coenzymes which were not additive over the single substitutions. Surprisingly, enzymes with changes at the two positions reduced efficiently acetaldehyde, displaying a K(m) value 10-fold lower and a catalytic efficiency sevenfold higher with respect to parent or singularly mutated enzymes. None of the engineered enzymes would convert formaldehyde, glutaraldehyde or aromatic aldehydes but all enzymes reduced propionaldehyde and butyraldehyde at relative reaction rates approximately half of that exhibited by acetaldehyde. Interestingly only mutant A274F was able to oxidize methanol almost as well as ethanol. In addition, this mutant was capable to convert secondary and cyclic alcohols, at a rate not detected in the other isoforms. These results are in general agreement with the prediction that increasing the size of amino acids in the proximity of the coenzyme pocket would hamper the accommodation of NADP but discord the increased affinity for NADPH as well as for alcoholic or aldehydic substrates with high steric hindrance.

The activity of yeast ADH I and ADH II with long-chain alcohols and diols

The activities of yeast ADH I and ADH II towards long chain alcohols and diols were studied using rather unusual conditions (1.0 M Tris pH 8.75, approximately 0.3 mg/ml enzyme and [S]<<<K(m) ) where the alcohols are oxidised quantitatively in a first-order manner. Plots of the apparent first-order rate constant versus primary alcohol chain length show double peaks with similar values for ethanol and 1-decanol and relatively low values for 1-butanol through to 1-octanol. With the alpha,omega diols only one peak of activity was observed with 1,14-tetradecanediol, the preferred substrate, being oxidised about the same rate as ethanol. Both enzymes were essentially inactive with short-chain diols (C(2)-C(8)). For all of these assays normalised rates with ADH II were about threefold faster than with ADH I.

Compartmentation protects trypanosomes from the dangerous design of glycolysis

Unlike in other organisms, in trypanosomes and other Kinetoplastida the larger part of glycolysis takes place in a specialized organelle, called the glycosome. At present it is impossible to remove the glycosome without changing much of the rest of the cell. It would seem impossible, therefore, to assess the metabolic consequences of this compartmentation. Therefore, we here develop a computer experimentation approach, which we call computational cell biology. A validated molecular kinetic computer replica was built of glycolysis in the parasite Trypanosoma brucei. Removing the glycosome membrane in that replica had little effect on the steady-state flux, which argues against the prevalent speculation that glycosomes serve to increase flux by concentrating the enzymes. Removal of the membrane did cause (i) the sugar phosphates to rise to unphysiologically high levels, which must have pathological effects, and (ii) a failure to recover from glucose deprivation. We explain these effects on the basis of the biochemical organization of the glycosome. We conclude (i) that the glycosome protects trypanosomes from the negative side effects of the "turbo" structure of glycolysis and (ii) that computer experimentation based on solid molecular data is a powerful tool to address questions that are not, or not yet, accessible to experimentation.

Electropulsation as an alternative method for protein extraction from yeast

The application of series of high intensity electric pulses to a yeast suspension provoked a considerable release of some cytoplasmic proteins, glutathione reductase, 3-phosphoglycerate kinase and alcohol dehydrogenase. A maximal yield was achieved 3-8 h after pulsation. The electro-induced protein efflux was accelerated by pretreatment with the reducing agent dithiothreitol and showed a strong dependence on the growth phase and the presence of monovalent ions in the post-pulse incubation medium. The results obtained for two strains of Saccharomyces cerevisiae, PV3 (diploid) and Y47 (wild haploid), showed that electropulsation can be used for the effective extraction of cytoplasmic proteins with a preserved functional activity.

Purification of alcohol dehydrogenase from Entamoeba histolytica and Saccharomyces cerevisiae using zinc-affinity chromatography

We have developed a single-step method for the purification of NADP(+)-dependent alcohol dehydrogenase from Entamoeba histolytica and NAD(+)-dependent alcohol dehydrogenase from Saccharomyces cerevisiae. It is based on the affinity for zinc of both enzymes. The amebic enzyme was purified almost 800 times with a recovery of 54% and the yeast enzyme was purified 30 times with a recovery of 100%. The kinetic constants of the purified enzymes were similar to those reported for other purification methods. With mammalian alcohol dehydrogenase, we obtained a 40-kDa band suggestive of purified alcohol dehydrogenase, but we failed to retain enzymatic activity in this preparation. Our results suggest that the described method is more applicable to the purification of tetrameric alcohol dehydrogenases.

Structural and biochemical studies of alcohol dehydrogenase isozymes from Kluyveromyces lactis

The cytosolic and mitochondrial alcohol dehydrogenases from Kluyveromyces lactis (KlADHs) were purified and characterised. Both the N-terminally blocked cytosolic isozymes, KlADH I and KlADH II, were strictly NAD-dependent and exhibited catalytic properties similar to those previously reported for other yeast ADHs. Conversely, the mitochondrial isozymes, KlADH III and KlADH IV, displayed Ala and Asn, respectively, as N-termini and were able to oxidise at an increased rate primary alcohols with aliphatic chains longer than ethanol, such as propanol, butanol, pentanol and hexanol. Interestingly, the mitochondrial KlADHs, at variance with cytosolic isozymes and the majority of ADHs from other sources, were capable of accepting as a cofactor, and in some case almost equally well, either NAD or NADP. Since Asp-223 of horse liver ADH, thought to be responsible for the selection of NAD as coenzyme, is strictly conserved in all the KlADH isozymes, this amino-acid residue should not be considered critical for the coenzyme discrimination with respect to the other residues lining the coenzyme binding pocket of the mitochondrial isozymes. The relatively low specificity of the mitochondrial KlADHs both toward the alcohols and the cofactor could be explained on the basis of an enhanced flexibility of the corresponding catalytic pockets. An involvement of the mitochondrial KlADH isozymes in the physiological reoxidation of the cytosolic NADPH was also hypothesized. Moreover, both cytosolic and KlADH IV isozymes have an additional cysteine, not involved in zinc binding, that could be responsible for the increased activity in the presence of 2-mercaptoethanol.

Identification of residues potentially involved in the interactions between subunits in yeast alcohol dehydrogenases

The lack of crystal structure for tetrameric yeast alcohol dehydrogenases (ADHs) has precluded, until now, the identification of the residues involved in subunit contacts. In order to address this question, we have characterized the thermal stability and dissociation propensity of native ADH I and ADH II isozymes as well as of several chimeric (ADH I-ADH II) enzymes. Three groups of substitutions affecting the thermostability have been identified among the 24 substitutions observed between isozymes I and II. The first group contains a Cys277-->Ser substitution, located at the interface between subunits in a three-dimensional model of ADH I, based on the crystallographic structure of the dimeric horse liver ADH. In the second group, the Asp236-->Asn substitution is located in the same interaction zone on the model. The stabilizing effect of this substitution can result from the removal of a charge repulsion between subunits. It is shown that the effect of these two groups of substitutions correlates with changes in dissociation propensities. The third group contains the Met168-->Arg substitution that increases the thermal stability, probably by the formation of an additional salt bridge between subunits through the putative interface. These data suggest that at least part of the subunit contacts observed in horse liver ADH are located at homologous positions in yeast ADHs.

Pyruvate decarboxylase of Zymomonas mobilis: isolation, properties, and genetic expression in Escherichia coli

Pyruvate decarboxylase (EC 4.1.1.1) from Zymomonas mobilis purified to homogeneity by using dye-ligand and ion-exchange chromatography. Antibodies produced against the enzyme and the amino-terminal sequence obtained for the pure enzyme were used to select and confirm the identity of a genomic clone encoding the enzyme selected from a genomic library of Z. mobilis DNA cloned into pUC9. The genomic fragment encoding the enzyme expressed high levels of pyruvate decarboxylase in Escherichia coli. Possible RNA polymerase and ribosome-binding sites have been identified in the 5'-untranslated region of the pyruvate decarboxylase gene.