Glycolytic enzymes activities

Entrala E, Mascaro C (1997) Glycolytic enzyme activities in Cryptosporidium parvum oocysts. FEMS Microbiol Lett 151 51-57... 

Szutowicz, A., Kwiatkowski, I. and Angielski, S., Lipogenetic and glycolytic enzyme activities in carcinoma and nonmalignant diseases of the human breast, Br J Cancer 39 (1979) 681-687. 

Intact plastids were isolated from early, early to mid and mid to late cotyledon embryos (1.5, 2.5 and 3.5 mg embryo fresh weight) of B. napus cv. Topas (according to [1]). Isolated plastids were incubated with " C-labelled metabolites and the incorporation of C into fatty acids determined [1]. The activities of enzymes were measured using standard assays [1] optimized for plastid extracts. The proportions of glycolytic enzyme activities attributable to the plastid were determined by adding increasing concentrations of cytosol (supernatant) back to a plastid pellet. The plastidial activity of each enzyme was then calculated from the relationship between its total activity and that of a cytosolic and plastidial marker enzyme essentially as previously described [3]. Short term assays for the rate at which isolated plastids take up Relabelled metabolites were performed using silicone oil filtration [4]. 

Although glucose uptake and glycolytic enzyme activity are homeo-statically regulated, glucose metabolism has also been shown to be regulated... 

A decreased glycolytic rate has been proposed as a cause of muscle fatigue and related to pH inhibition of glycolytic enzymes. Decreasing pH inhibits both phosphorylase kinase and phosphofructokinase (PFK) activities. PFK is rate determining for glycolytic flux and therefore must be precisely matched to the rate of ATP expenditure. The essential characteristic of PFK control is allosteric inhibition by ATP. This inhibition is increased by H and PCr (Storey and Hochachka, 1974 ... 

Triose phosphate isomerase (TPI) catalyzes the interconversion of glyceralde-hyde-3-phosphate and dihydoxyacetone phosphate and has an important role in glycolysis, gluconeogenesis, fatty acid synthesis, and the hexose monophosphate pathway. Red blood cell TPI activity measured in vitro is approximately 1000 times that of Hx, the least active glycolytic enzyme. TPI is a dimer of identical subunits, each of molecular weight 27,000, and does not utilize cofactors or metal ions. Posttranslational modification of one or both subunits may occur by deamidination, resulting in multiple forms of the enzymes and creating a complex multibanded pattern on electrophoresis. 

To give rise to oscillatory behavior instead of a biochemical explosion, selfamplification must, however, be coupled to a limiting process. Such a limiting process can be viewed as a form of negative feedback because it occurs as a consequence of the positive feedback that precedes it. Thus, in the case of glycolytic oscillations, the activation of phosphofructokinase by a reaction product is followed by a counteracting fall in the rate of the enzymatic reaction, due to the enhanced substrate consumption associated with enzyme activation. In Ca + pulsatile signaling, the explosive rise in cytosolic Ca + due... 

Cycles arise becanse both the glycolytic and gluconeogenic enzymes are simnltaneously active. Consequently, an increase in gluconeogenic flux can be achieved either by a decrease in the activity of the glycolytic enzyme(s) and/or an increase in the activity of the gluconeogenic enzyme(s). 

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