Liquid-liquid partitioning of some enzymes, especially phosphofuctokinase, from Saccharomyces cerevisiae at subzero temperature

The effects of low temperature (−18°C) on the stability and partitioning of some glycolytic enzymes within an aqueous two-phase system were studied. The enzymes were phosphofructokinase, glyceraldehyde-3-phosphate dehydrogenase and alcohol dehydrogenase present in a crude extract of bakers' yeast. The partitioning of pure phosphofructokinase, isolated from bakers' yeast, was also examined. The two-phase systems were composed of water, poly(ethylene glycol), dextran, and ethylene glycol and buffer. The influence on the partitioning of the presence of ethylene glycol, phenylmethylsulfonyl fluoride and poly(ethylene glycol)-bound Cibacron Blue F3G-A was investigated at −18, 0 and (in some cases) 20°C. The presence of ethylene glycol, phase polymers and low temperature stabilized all three enzyme activities. Cibacron Blue, an affinity ligand for phosphofructokinase, increased its partitioning into the upper phase with decreasing temperature. Depending on the conditions, various amounts of the enzymes were recovered at the interface, also in systems not containing ethylene glycol. The implications of the observed effects on the use of aqueous two-phase systems for the extraction and fractionation of proteins are discussed.     

Trypanosoma brucei: activities and subcellular distribution of glycolytic enzymes from differently disrupted cells

The effect of disruption procedure on the subcellular distribution and the activities of 11 enzymes catalyzing the glycolytic pathway in Trypanosoma brucei has been studied. The activities of the enzymes varied with the lytic procedure used. Maximum specific enzyme activity values were obtained after treatment with saponin whereas digitonin treatment gave the lowest results. The intracellular location of the enzymes was examined by means of differential centrifugation following cell lysis with saponin, Triton X-100, digitonin, or by freezing and thawing. Irrespective of the method of cell lysis employed, the six enzymes, hexokinase, phosphofructokinase, aldolase, phosphoglycerate kinase, glycerol phosphate dehydrogenase, and glycerokinase, were particulate. Of the remaining 5 enzymes, digitonin liberates only phosphoglycerate mutase (partially); saponin or Triton X-100 liberates phosphoglucose isomerase, phosphoglycerate mutase, enolase, and pyruvate kinase but not glyceraldehyde 3-phosphate dehydrogenase; freezing and thawing acts like saponin or Triton X-100 except that it fails to liberate phosphoglucose isomerase, while cell grinding with silicon carbide liberates only glyceraldehyde phosphate dehydrogenase (partially), phosphoglycerate mutase, enolase, and pyruvate kinase. The relative maximal activities of the enzymes suggest that the rate-limiting steps in glycolysis in T. brucei are the reactions catalyzed by aldolase and phosphoglycerate mutase.     

Phosphofructokinase activities within the order Spirochaetales and the characterisation of the pyrophosphate-dependent phosphofructokinase from Spirochaeta thermophila

The subtype of phosphofructokinase activity, either ATP-, ADP- or pyrophosphate-dependent, present in members of three genera from the Spirochaetales was investigated. The individual species/strains examined included Spirochaeta alkalica, S. asiatica, S. halophila, S. isovalerica, S. litoralis, S. zuelzerae, S. thermophila, two thermophilic spirochetes, Treponema bryantii, T. denticola, paragraph signT. pectinovorum, Leptospira biflexa and L. interrogans. All of the Spirochaeta strains, regardless of their phenotype, possessed primarily a pyrophosphate-dependent phosphofructokinase. In contrast, T. bryantii, T. denticola and L. biflexa had predominantly an ATP-dependent activity, whereas no activity was detected in T. pectinovorum or paragraph signL. interrogans. The results suggest that pyrophosphate-dependent phosphofructokinase activity may be a reliable phenotypic marker for the genus Spirochaeta and that there are potentially interesting differences in how the catabolism of saccharides is controlled among members of genera within the Spirochaetales. The pyrophosphate-dependent phosphofructokinase from S. thermophila strain RI 19.B1 was purified (303-fold) to homogeneity and biochemically characterised. The S. thermophila enzyme displayed hyperbolic kinetics with respect to both the forward and reverse cosubstrates and was not significantly affected by traditional activators or inhibitors of phosphofructokinase. The biochemical characterisation represents the first spirochete phosphofructokinase to be described.     

Influence of a sulfhydryl cross-link across the allosteric-site interface of E. coli phosphofructokinase

To assess the role of quaternary stability on the properties of Escherichia coli phosphofructokinase (PFK), a disulfide bond has been introduced across the subunit interface containing the allosteric binding sites in E. coli phosphofructokinase by changing N288 to cysteine. N288 is located in close proximity to the equivalent residue on an adjacent subunit. Although SDS-PAGE of oxidized N288C indicates monomeric protein, blocking the six native cysteine residues with N-ethyl maleimide (NEM) reveals dimers of N288C on non-native gels. Subsequent addition of dithiothreitol (DTT) to NEM-labeled N288C regenerates the monomer on SDS-PAGE, reflecting the reversibility of intersubunit disulfide bond formation. KSCN-induced hybrid formation between N288C and the charged-tagged mutant E195,199K exhibits full monomer-monomer exchange only upon DTT addition, providing a novel assessment of disulfide bond formation without NEM treatment. N288C also exhibits a diminished tendency toward nonspecific aggregation under denaturing conditions, a phenomenon associated with monomer formation in PFK. Pressure-induced dissociation and urea denaturation studies further indicate that oxidized N288C exhibits increased quaternary stability along both interfaces of the tetramer, suggesting a synergistic relationship between active site and allosteric site formation. Although the apparent binding affinities of substrates and effectors change somewhat upon disulfide formation in N288C, little difference is evident between the maximally inhibited and activated forms of the enzyme in oxidizing versus reducing conditions. Allosteric influence, therefore, is not correlated to subunit-subunit affinity, and does not involve substantial interfacial rearrangement.     

Plant-like phosphofructokinase from Plasmodium falciparum belongs to a novel class of ATP-dependent enzymes

Malaria parasite-infected erythrocytes exhibit enhanced glucose utilisation and 6-phospho-1-fructokinase (PFK) is a key enzyme in glycolysis. Here we present the characterisation of PFK from the human malaria parasite Plasmodium falciparum. Of the two putative PFK genes on chromosome 9 (PfPFK9) and 11 (PfPFK11), only the PfPFK9 gene appeared to possess all the catalytic features appropriate for PFK activity. The deduced PfPFK proteins contain domains homologous to the plant-like pyrophosphate (PPi)-dependent PFK β and α subunits, which are quite different from the human erythrocyte PFK protein. The PfPFK9 gene β and α regions were cloned and expressed as His₆- and GST-tagged proteins in Escherichia coli. Complementation of PFK-deficient E. coli and activity analysis of purified recombinant proteins confirmed that PfPFK9β possessed catalytic activity. Monoclonal antibodies against the recombinant β protein confirmed that the PfPFK9 protein has β and α domains fused into a 200 kDa protein, as opposed to the independent subunits found in plants. Despite an overall structural similarity to plant PPi-PFKs, the recombinant protein and the parasite extract exhibited only ATP-dependent enzyme activity, and none with PPi. Unlike host PFK, the Plasmodium PFK was insensitive to fructose-2,6-bisphosphate (F-2,6-bP), phosphoenolpyruvate (PEP) and citrate. A comparison of the deduced PFK proteins from several protozoan PFK genome databases implicates a unique class of ATP-dependent PFK present amongst the apicomplexan protozoans.     

Plasmodium knowlesi: glycolytic intermediate levels of enzyme activities of infected rhesus monkey erythrocytes

In vitro glycolytic enzyme activities and in vivo glycolytic intermediate concentrations were assayed in Plasmodium knowlesi-infected rhesus monkey erythrocytes and control erythrocytes. The enzyme activities of infected erythrocytes were greater than controls indicating that P. knowlesi had its own glycolytic system and that parasite glycolysis was the source of the increased rate of glucose consumption by infected erythrocytes. The P. knowlesi glycolytic enzymes phosphofructokinase and hexokinase were less sensitive to acid inhibition than uninfected red cells.P. knowlesi-infected monkey erythrocytes and Plasmodium berghei-infected mouse erythrocytes had similar in vivo glycolytic profiles and in vitro enzyme activity increases.     

Effect of low temperature on the activity of phosphofructokinase from potato tubers

The aim of this work was to compare the coldlability of phosphofructokinase (EC 2.7.1.11) from tubers of potato cultivars (cvs.) known to differ in their propensity to accumulate sugars at low temperature. When stored at 4°C for six weeks, the sugar content of tubers ofSolanum tuberosum L. cv. Record doubled whereas the amount of sugar in tubers of cv. Brodick and an advanced breeding clone (13676) decreased slightly. Tubers from each line contained four forms of phophofructokinase. Over the range 12°–16°C the temperature coefficients of the four forms of phosphofructokinase from cvs. Record and Brodick were similar. In cv. Record the temperature coefficients of three of the enzyme forms were significantly higher at 2°–6°C than at 12°–16°C, whereas those from cv. Brodick were unchanged. These results are consistent with the proposal that inactivation of phosphofructokinase at low temperature results in the accumulation of hexose phosphates leading to increased sucrose synthesis.     

Ultrastructural alterations in Saccharomyces cerevisiae cells in association with elevated temperature-induced autolysis

By means of the freeze-etching technique ultrastructural alterations in Saccharomyces cerevisiae cells undergoing autolysis at elevated temperature were studied. Wall surfaces of intact cells were smooth. During autolysis wall surfaces became rough with granules of 20-40 nm diameter. This alteration occurred after extensive disintegration of cytoplasmic organelles and after functional and ultrastructural impairments of the plasma membrane, but well before the rupture of the plasma membrane.