Glycolytic enzyme complex

Pyruvate produced by the glycolytic pathway may be transported into the mitochondria (via an antiport with OH"), where it is converted to acetyl-CoA by the action of the enzyme complex pyruvate dehydrogenase. The pertinent enzyme activities are pyruvate dehydrogenase (PD), lipoic acid acetyltransferase, and dihydrolipoic acid dehydrogenase. In addition, several cofactors are utilized thiamine pyrophosphate (TPP), lipoic acid, NAD+, Co A, and FAD. Only Co A and NAD+ are used in stoichiometric amounts, whereas the others are required in catalytic amounts. Arsenite and Hg2+ are inhibitors of this system. The overall reaction sequence may be represented by Figure 18.5. The NADH generated may enter the oxidative phosphorylation pathway to generate three ATP molecules per NADH molecule reduced. The reaction is practically irreversible its AGq = -9.4 kcal/mol. 

Brooks, S. P. J. Storey, K. B. (1991a). A quantitative evaluation of the effect of enzyme complexes on the glycolytic rate in vivo mathematical modeling of the glycolytic complex. J. Theor. Biol. 149, 361-368. 

The complex oscillations predicted by the model can be related to those sometimes observed, at low values of the substrate injection rate, in glycolysing yeast extracts. Such complex glycolytic oscillations (fig. 4.31) could represent chaos resulting from the interaction between oscillating phosphofructokinase and a second instability-generating reaction, catalysed by another glycolytic enzyme, in a small range of values of the substrate injection rate. 

The extension of the network in eqns (1.5 a-e) to multiple intermediates is Important in devising plausible multi-enzyme rate forms for microbial metabolism. The Henri form obtained in eqns (1.5a-e) involves three different enzyme complexes, all equilibrated with each other "upstream to the kinetically slow step (eqn (1.3)). The negligible free energy changes evident for many of the steps in the Embden-Meyerhof glycolytic sequence (Figure 1) indicate that the three reaction sequences (1.7a,b,c),... 

The glycolytic pathway described in this chapter begins with the breakdown of glucose, but other sugars, both simple and complex, can enter the cycle if they can be converted by appropriate enzymes to one of the intermediates of glycolysis. Figure 19.32 shows the mechanisms by which several simple metabolites can enter the glycolytic pathway. Fructose, for example, which is pro-... 

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. 

In contrast to milk, where samples are primarily derived from cows, meat analysis has to be performed in samples of a widely different animal origin including cattle, lamb, swine, poultry, and fish. Muscle is a complex matrix with a pH of 5.7, composed of muscle fibers, various types of connective tissue, adipose tissue, cartilage, and bones. Sarcoplasmic proteins such as myoglobin, and glycolytic enzymes are soluble in water while the myofibrillar proteins such as myosin and actin are soluble in concentrated salt solutions (14). The connective tissue proteins, collagen and elastin, are insoluble in both solvents. 

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