Origin of multiple species of yeast enolase A on isoelectric focusing

Gradient chromatofocusing-mass spectrometry: a new technique in protein analysis

A new analytical technique, gradient chromatofocusing-mass spectrometry (gCF-MS), was developed employing ion-exchange high-performance liquid chromatography (HPLC) interfaced to an electrospray-quadrupole mass spectrometer in the determination of proteins. There have been few reports, if any, of a HPLC-MS technique for proteins in which the ion-exchange column is directly interfaced to the mass spectrometer. The employment of a linear pH gradient elution scheme directly interfaced to mass spectrometry is also unique in the present work. The technique was demonstrated by the separation of six proteins (carbonic anhydrase II, enolase, beta-lactoglobulin A, lactoglobulin B, soybean trypsin inhibitor, and amyloglucosidase) employing a descending linear pH gradient from pH 9 to 2.6 on a 50 mm x 2.1 mm DEAE HPLC column using volatile buffer components. A signal enhancement solution consisting of 8% formic acid in acetonitrile was pumped post-column and was mixed 1:1 with column effluent and then directed on-line into the mass spectrometer. Molecular masses of the proteins were determined within +/-0.010% to 0.033% (+/-100 to 330 ppm) with peak height total ion current detection limits of 4 to 78 pmol of injected amounts (S/N = 3). This technique is applicable to the analysis of proteins and other charged molecules.

Plants contain highly divergent actin isovariants

Actin protein isovariants have been identified in animals with distinct cytoplasmic or muscle specific patterns of expression. Analysis of vascular plant actin gene sequences suggests that an even greater diversity should exist within the plant actin protein families, but previous studies on plant proteins have not demonstrated the presence of multiple actin isovariants. Antibodies recognizing a conserved amino-terminal plant actin peptide, a family of plant actin peptides from a variable region, and two monoclonal antibodies to conserved epitopes within animal actins were used to identify isovariants of soybean actin resolved by two-dimensional isoelectric focusing (IEF) sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Approximately six to eight actin isovariants with pI values ranging from 5.1 to 5.8 have been identified from soybean hypocotyls, stems, leaves, and roots with varying amounts of most isovariants present in all four organs. Acidic isovariants were present in much higher levels in leaves and stems. Antisera with lambda-class actin specificity detected a subset of three isovariants in all organs examined. One monoclonal and one antipeptide antisera are shown to react well with a wide variety of plant actin isovariants. Similar patterns of actin isovariants were detected in the distant angiosperms, Arabidopsis, petunia, and maize. It is likely that many of these diverse classes of isovariants have been preserved throughout vascular plant evolution and reflect the ancient diversity within plant actin gene families. The extreme difference among isovariants implies the presence of a complex actin-based cytoskeletal system in plants.

Purification of three distinct enolase isoenzymes from yeast

A method for the rapid isolation of yeast enolases, yielding three distinct isoenzymes, has been devised. In the first step anionic proteins were precipitated with polyethyleneimine, whereas hydrophobic enolase isoenzymes remained in the supernatant. Secondly, the supernatant was 45% saturated with ammonium sulfate and bound to phenyl-Sepharose CL-4B. Decreasing ammonium sulfate and simultaneously increasing ethylene glycol concentrations were used for elution. Finally, enolase isoenzymes were separated by chromatofocusing. The purified isoenzymes gave single bands after isoelectric focusing.

Binding of fluoride by yeast enolase

The kinetics of fluoride binding by yeast enolase have been examined by direct measurement of equilibrium fluoride (F) concentrations with an ion-specific electrode. Mg2+ and inorganic phosphate (Pi) affect the binding of F, and evidence is presented for an ordered binding mechanism in which phosphate and F interact with conformational and catalytic Mg2+ species, with the overall formation of a quaternary complex. A maximum of four atoms of F were bound per enzyme dimer, and the data point to the nonequivalent binding of pairs of F atoms. The dissociation constants were 5.0 X 10(-4) M and 8.2 X 10(-5) M for the first and second pairs of F atoms, respectively. The first pair of binding sites was filled when the ratio of phosphate ions/enolase dimer exceeded 2 and appeared to involve the pair of conformation Mg2+ ions. The binding of the second pair of F atoms followed the binding of catalytic Mg2+ in the presence of Pi and, furthermore, appeared to exhibit positive cooperativity with respect to F. The data suggest, also, that the binding of Pi may involve sequential addition of Pi pairs to the different Mg2+ species on the enzyme. F binding was at a maximum between pH 5.5 and pH 6.0, consistent with an involvement of the monovalent form of Pi. In the absence of added Pi, (MgF)+ appeared to be the preferred ligand. Addition of the enzyme substrate 2-phosphoglycerate led to the release of bound F. These findings are consistent with the known patterns of inhibition of enzymatic activity by F.

Yeast enolase: mechanism of activation by metal ions

Yeast enolase as prepared by current procedures is inherently chemically homogeneous, though deamidation and partial denaturation can produce electrophoretically distinct forms. A true isozyme of the enzyme exists but does not survive the purification procedure. The chemical sequence for both has been established. The enzyme behaves in solution like a compact, nearly spherical molecule of moderate hydration. Strong intramolecular forces maintain the structure of the individual subunits. The enzyme as isolated is dimeric. If dissociated in the presence of magnesium ions and substrate, then the subunits are active, but if the dissociation occurs in the absence of metal ions, they are inactive until they have reassociated and undergone a first order "annealing" process. Magnesium (II) enhances association. The interaction between the subunits is hydrophobic in character. The enzyme can bind up to 2 mol of most metal ions in "conformational" sites which then allows up to 2 mol of substrate or some substrate analogue to bind. This is not sufficient for catalysis, but conformational metal ions do more than just allow substrate binding. A change in the environment of the metal ions occurs on substrate or substrate analogue binding. There is an absolute correlation between the occurrence of a structural change undergone by the 3-amino analogue of phosphoenolpyruvate and whether the metal ions produce any level of enzymatic activity. For catalysis, two more moles of metal ions, called "catalytic", must bind. There is evidence that the enzymatic reaction involves a carbanion mechanism. It is likely that two more moles of metal ion can bind which inhibit the reaction. The requirement for 2 mol of metal ion per subunit which contribute in different ways to catalysis is exhibited by a number of other enzymes.

Effect of aging on enolase from rat muscle, liver and heart

Muscle enolase (2-phospho-D-glycerate hydrolase, EC 4.2.1.11) and liver enolse from young and old rats have been purified to homogeneity and several properties of the respective young/old pairs, including Km, behavior on polyacrylamide gels, sensitivity to heat and specific activity have been compared. No difference has been detected. On the other hand, the heart isozyme shows an age-related increase in a heat-sensitive form of the enzyme. The results strongly support the idea tht some enzymes become altered in aging animals but others do not.