Specific Activity Of Phosphofructokinase Research Articles

The role of glycolysis in aflatoxin biosynthesis.

In resting mycelia of Aspergillus parasiticus NRRL 3240, all the glycolytic intermediates with the exception of glucose and phosphoenolpyruvate stimulated the de novo synthesis of aflatoxin from exogenous acetate. Intracellular levels of glycolytic intermediates were measured in the toxigenic strain, A. parasiticus NRRL 3240, and the nontoxigenic strain, A. flavus NRRL 3537. In 48-h cultures, the concentrations of the intermediates beyond the phosphofructokinase reaction were higher in toxigenic mycelial extracts than in nontoxigenic cultures. There was a marked reduction in the specific activity of phosphofructokinase with increasing age in the toxigenic strain. The specific activity of this enzyme was two- to four-fold lower in zinc-deficient mycelia of A. parasiticus. In resting cultures, the uptake rate of labeled glucose was considerably lower in zinc-deficient mycelia than in zinc-replete or nontoxigenic cultures. On the basis of the results obtained, it can be said that intense formation of aflatoxin is associated with a sharp fall in the level of phosphoenolpyruvic and pyruvic acids. This was accompanied by a significantly higher pyruvate kinase activity.

Partial separation and biochemical characteristics of periportal and perivenous hepatocytes from rat liver.

Suspensions of enzymatically prepared hepatocytes from starved rats were separated according to their buoyant density at 12 degrees C in linear, isosmotic gradients of metrizamide, centrofuged at low speed for a relatively short time. The recovery of cell protein was 86%. Hepatocytes of high viability formed a single band around 1.10 g/cm3 and were recovered as four density populations (P1-P4) form low to high density, respectively. The content of protein was significantly lower in population P1, while the content of neutral fat or the averaged cell size was similar in the various populations. The specific activity of alanine aminotransferase increased in the order P1-P4. The distribution of this enzyme within the intact liver acinus obtained by others indicate that a partial separation of periportal and perivenous hepatocytes had occurred. The activity patterns of lactate dehydrogenase, glutamate dehydrogenase, isocitrate dehydrogenase (NADP+) and pyruvate kinase, also with known intra acinar distributions, supported this conclusion. The hepatocytes showed signs of shrinkage after separation, but since they retained a normal ultrastructure, most enzyme activities and viability, the present technique was regarded superior to previous procedures of hepatocyte separation by density. The degree of separation was calculated from an equation (see Appendix), and the periportal/perivenous ratio for parameters measured in density populations can be obtained. The specific activity of phosphofructokinase, alcohol dehydrogenase and aldehyde dehydrogenase showed no differences between populations. However, the ratio high-Km/low-Km aldehyde dehydrogenase increased in the order P4-P1.

Some effects of medroxyprogesterone acetate on intermediary metabolism in rat liver

Specific activities of phosphofructokinase (PFK), pyruvate kinase (PK), glycerol-3-phosphate dehyrdogenase (G3PD), “malic” enzyme (ME), and glucose-6-phosphate dehydrogenase (G6PD), were studied in rats treated with medroxyprogesterone acetate (MPA). The effects of saline and of cortisol were studied for comparison. Reduced nicotinamide adenine dinucleotide phosphate (NADPH) activity was also estimated in all three groups. The elevation of ME, NADPH, and G3PD suggest the possibility of lipogenic stimulation by MPA. Since no change could be detected in PFK, PK and G6PD following MPA therapy, the elevation of ME and NADPH activities may also reflect increased amino acid conservation. MPA treatment results in an enzymatic pattern distinctly different from that produced by cortisol.

Effect of pollination on protein metabolism and enzyme activity in young fruits of Citrullus lanatus

Summary Protein synthesis was investigated in watermelon ovaries by measuring incorporation of L- (G-H3) leucine into protein during 48 hr periods after pollination or treatment of ovaries with NAA. During the first six days of fruit growth at least 80% of proteins were synthesised in flesh and pericarp rather than ovules. Increases in cellulase activity were not directly correlated with growth by cell expansion; between Days 0 and 9 specific activities increased 2-fold in seeded fruit, did not change in parthenocarpic fruit and increased 4-fold in non-pollinated ovaries. During the same period there was a 1.7-fold increase in specific activity of glucose 6-phosphate dehydrogenase in seeded and parthenocarpic fruit but no change in specific activity of phosphofructokinase. In non-pollinated ovaries specific activities of glucose 6-phosphate dehydrogenase did not exceed activities present in ovaries at anthesis. However, in non-pollinated ovaries after six days, there was a coincident decrease in specific activity of glucose 6-phosphate dehydrogenase and increase in specific activity of phosphofructokinase. The possible significance of these changes is discussed.

Investigations on phosphofructokinase (PFK, EC 2.7.1.11) in bovine lenses in dependence on age, topographic distribution and water soluble protein fractions

The specific activity of phosphofructokinase and its affinity to the substrate fructose-6-phosphate was determined with reference to the age of lens. The allosteric behaviour of the enzyme was eliminated by choosing the appropriate assay conditions. Age-dependent changes could be observed in both parameters. The specific activity decreased by 50% during the first 4 years, thereafter remaining almost constant. It was highest in the lens equator followed by anterior and posterior cortical region and lens nucleus. The substrate saturation curve for the calf lens shows a typical hyperbolic course, (Michaelis-Menten) and the slope of Lineweaver-Burk plot gives a K m -value of 5 × 10 −5 m for F-6-P. For the nucleus of calf and bovine lenses the Lineweaver-Burk diagram shows convex curves indicating heterogeneity of the kinetic properties due to aging. After separation of the water soluble proteins the activity of phosphofructokinase could be localized in the α-crystallin as well as in the β-crystallin fraction.

Enzymes of Dictyuchus monosporus

A number of morphological and reproductive similarities between members of the genus Dictyuchus and those of Achlya prompted the present study of enzyme activities of Dictyuchus monosporus. Specific activities of phosphofructokinase, aldolase, isocitrate dehydrogenase, malate dehydrogenase, cytochrome oxidase, glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, lactate dehydrogenase, alcohol dehydrogenase, and catalase in Dictyuchus were determined. The activities found were in general comparable to those found in Achlya ambisexualis, with the exceptions of glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, whose activities were considerably lower in Dictyuchus.

Some kinetic properties of Mucor rouxii phosphofructokinase : Effect of cyclic adenosine 3′,5′-monophosphate

Phosphofructokinase activity was detected in extracts from mycelium and yeast cells of the dimorphic fungus Mucor rouxii. The specific activity of phosphofructokinase is strongly dependent on fungus morphology, being 30–40 times higher in yeast extracts than in extracts of mycelium grown in a medium devoid of glucose. These findings are in agreement with the type of metabolism in both forms of the fungus. Phosphofructokinase is inhibited by excess of ATP and by citrate. Both inhibitions are overcome by cyclic adenosine 3′,5′-monophosphate. The probable involvement of phosphofructokinase in controlling morphogenesis in Mucor rouxii and its interaction with cyclic adenosine 3′,5′-monophosphate is suggested.

Protein Degradation during Yeast Sporulation Enzyme and Cytochrome Patterns

The levels of several enzymes have been studied during sporulation of Saccharomyces cerevisia. The specific activities of ribonuclease and aminopeptidase I raised several-fold after transfer of the cells to sporulation medium, whereas the specific activities of phosphofructokinase, glucose-6-phosphate dehydrogenase, tryptophan synthase and pyruvate decarboxylase were not significantly altered. The specific activities of NAD-dependent glutamate dehydrogenase, isocitrate lyase, malate dehydrogenase and fructose bisphosphatase all decreased from the onset of sporulation. The inactivation of these latter enzymes was inhibited by cycloheximide and by inhibitors of energy metabolism. Hexokinase, alcohol dehydrogenase and glutamate oxaloacetate transaminase were partially lost from the cells during the period of ascus maturation. None of the enzyme changes observed proved to be 'sporulation-specific' in that it occurred exclusively in sporulating diploid yeast cells. Therefore it is postulated that the meiotic events and the metabolic changes required for ascospore formation are under separate genetic control in this organism. During sporulation, the cellular content of cytochromes b, c, and aa3 was reduced to 20% or less of that present in vegetative derepressed cells. Since the relative percentage of total to cycloheximide-insensitive mitochondrial protein synthesis was not significantly altered throughout sporulation, and the pattern of mitochondrially synthesized polypeptides was rather similar both in vegetative and in sporulating cells, it appeared that not only degradation but also synthesis and therefore turnover of the mitochondrially coded polypeptides of cytochromes b and aa3 took place during sporulation. The activity ratio of cytochrome c oxidase to F1-ATPase in submitochondrial particles isolated from vegetative cells and from purified asci was almost identical. This indicates that the loss of membrane-bound mitochondrial cytochromes during sporulation is probably due to a nonselective degradation of inner mitochondrial membrane proteins.