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At least 19 recordsLinked to original sources
PubMed2000

Purification, molecular and kinetic characterization of phosphofructokinase-1 from the yeast Schizosaccharomyces pombe: evidence for an unusual subunit composition.

Phosphofructokinase-1 (Pfk-1) from Schizosaccharomyces pombe was purified by 54-fold enrichment to homogeneity elaborating the following steps: (a) Disruption of the cells with glass beads; (b) fractionated precipitation with polyethylene glycol 6000; (c) affinity chromatography on Cibacron-Blue F3G-A-Sephadex G 100; (d) ion exchange chromatography on Resource Q. The native enzyme exhibits a mass of 790+/-30 kDa, as detected by sedimentation equilibrium measurements. The apparent sedimentation coefficient was found to be s(20,c)=20.2+/-0.3 S. No significant dependence of the s-value on the protein concentration was observed in the range 0. 07-0.7 mg/ml. Polyacrylamide gel electrophoresis in presence of sodium dodecyl sulphate and MALDI-TOF spectra showed that the enzyme is composed of subunits of identical size of 100+/-5 kDa, forming an octameric structure. The N-terminus of the enzyme was found to be blocked. Sequences of tryptic and chymotryptic peptides of the subunit coincide with the proposed amino acid sequence as deduced from the gene from the EMBL library. The Pfk-1 coding sequence of S. pombe was transformed into a Pfk-1 double deletion mutants of Saccharomyces cerevisiae resulting in glucose-positive cells with enzyme activity in the crude cell extract. The kinetic analysis revealed less cooperativity to fructose 6-phosphate (n(H)=1.6) and less inhibition by ATP as compared to the enzyme from baker's yeast. Fructose 2,6-bisphosphate (in micromolar range) and AMP (in millimolar range) were found to overcome ATP inhibition and to increase the affinity to fructose 6-phosphate.

Adenosine Monophosphate↗
PubMed1975

The roots of bioenergetics.

Understanding metabolic energy transformation began with the realization of an 'intrusion' of phosphate into the mechanism of alcoholic fermentation. The discovery of an analogous participation of phosphate in muscle glycolysis connected the metabolic generation of energy-rich phosphate bonds fed into a common transmitter, adenosine triphosphate (ATP), with the production of mechanical energy through the finding that the phosphoryl group of creatine phosphate transferred to ATP could supply the energy for muscle contraction. In this way, a functional applicability of the energy of the phosphate bond was first shown. This observation was soon followed by the recognition that the phosphoanhydride bond of ATP provided the driving force in biosynthetic reactions; in this type of bond, metabolic energy apparently collects before it is transmitted for functional and biosynthetic use. The storage of energy in ATP was first detected in anaerobic energy-yielding reactions but soon was also found in respiratory and photosynthetic energy production. However, the mechanism by which energy derived from metabolites was converted into phosphate-bond energy in the latter processes appeared to differ from that of anaerobic energy transmission. Whereas phosphorylated compounds mediate the latter in homogeneous solutions, aerobic phosphorylation and photophosphorylation in prokaryotes seem to require special submembranous structures; and in eukaryotes, energy conversion is a function of special organelles, the mitochondria and chloroplasts. The evolutionary aspects of the transition from prokaryotes to eukaryotes are of considerable interest. In conclusion, the relevance of an apparent prokaryotic origin of the energy-transforming organelles in the eukaryotes will be commented on.

Adenosine Triphosphatases↗
PubMed1975

Energy utilization for control.

When, on addition of a suitable substrate, a chemical potential is applied to an enzymic process such as glycolysis or respiration, whether in solution or membrane-bound, all components of the process pass into a nonequilibrium state, which might be steady or non-steady and which produces the following phenomena: (1) The reactants of each enzymic reaction are displaced from their equilibrium concentration, and energy is dissipated; (2) Part of each enzyme is transferred to a transition state of its catalytic function as well as isosteric and allosteric controlling functions, displaying local and gross conformation changes, and a rate-controlling state is generated; (3) In cyclic portions of a process futile events and chemical interconversion may occur; (4) In self- and cross-coupled portions of a process, oscillation with periodic changes of states and spatial propagation as well as instabilities may be observed; (5) At each step of a process, depending on the rate of flux and the specific enzymic function, a varying proportion of the free energy changes--which are concentration-dependent and derived from the overall potential of the system-is contributed to the control of flux rates. This will be exemplified for enzymes of bioenergetic pathways.

Adenosine Triphosphate↗
PubMed1994

Fructose metabolism and cell survival in freshly isolated rat hepatocytes incubated under hypoxic conditions: proposals for potential clinical use.

The protective effect of fructose with regard to hypoxia-induced cell injury was investigated. The addition of fructose (2 to 20 mmol/L) protected hepatocytes against hypoxia-mediated cell lysis in a concentration-dependent way. The intracellular ATP content was initially decreased as a result of fructose-1-phosphate formation, but it remained constant during the hypoxic incubation. Conversely, high initial ATP values observed at low fructose concentrations progressively declined. Cellular protection was observed only when fructose was added before (and not after) the start of hypoxia. In addition, a sufficient amount of fructose-1-phosphate rapidly accumulated before the induction of hypoxia, and the linear production of lactate, during hypoxic incubation, indicated that cells synthesized ATP continuously. The lack of cell protection by fructose added after the onset of the hypoxia may be explained by a lesser fructose-1-phosphate formation and a subsequently low accumulation leading to insufficient glycolytic ATP production. Under aerobic conditions, both glycolysis (lactate formation) and gluconeogenesis (glucose formation) were carried out in fructose-1-phosphate-loaded cells with the same initial rates, whereas under hypoxic conditions glycolysis was the main metabolic event. The fact that protein synthesis activity recovered faster during reoxygenation of previously hypoxic fructose-treated cells than in glucose-treated cells led us to hypothesize that in situ perfusion of liver with fructose, before its removal, would improve its metabolic capacity during the hypoxic cold preservation and subsequent transplantation.

Adenosine Triphosphate↗