Fasting state enzymes

The body has 3 periods when creatine uptake is highest After a nights sleep, the body is in a fasted stated due to a period of natural GH pulses (about half of your daily total GH production is released during the first 4 hours of sleep) and a prolonged period without nutrients. This results in an up-regulation of nutrient transporters and enzymes which favor intramuscular uptake of nutrients, including Creatine. 

Fatty add synthetase is not controlled directly by phosphorylation however, insulin, glucagon, and thyroxine have an effect on its activity by controlling its cellular concentration. Both insulin and thyroxine increase the biosynthesis of the enzyme, whereas glucagon is inhibitory. Thyroxine and glucagon appear to regulate the biosynthesis at the transcription level, whereas insulin affects the enzyme activity at the translation level. It has no effect on cellular fatty add synthetase mRNA concentration. In summary, fatty add synthetase levels are up in the fed state and down in the fasting state. 

Enzyme pyruvate kinase. Pyruvate kinase is more active in the fed state than in the fasting state. 

D. Insulin causes activation of phosphatases, which dephosphorylate all of the enzymes that were phosphorylated in the fasting state. Protein kinase A is not activated by phosphorylation during fasting but by the binding of cAMP to regulatory subunits. 

Residual activity of purified HGL or HGL in gastric juice has been tested after the enzyme was incubated for 2 h at various pH values (Ville et al., 2002). In between pH 2 and 6-7, HGL remains highly stable in gastric juice with a recovery of h-pase activity as high as 93%. For extreme pH values, the activity decreases rapidly (pH 8) or is definitely lost (pH 0.5, 0.75 and 1) which means that basal HGL secreted in fhe fasting state is most likely inactivated and that the buffering effect of a meal seems compulsory to preserve HGL activity. Pure HGL is more pH-sensi-... 

Glucokinase is also an inducible enzyme. The concentration of the enzyme increases in the fed state, when blood glucose and insulin levels are elevated, and decreases in the fasting state, when glucose and insulin are low. 

If a reaction is spontaneous, does that mean it will be fast Thermodynamic spontaneity cannot tell us whether a reaction will he fast. The speed of a reaction is a kinetic property controlled hy the nature of the energy state of the ES complex and the transition state. Enzymes speed up the reaction rate by creating a situation where the distance between the transition state and the ES complex on an energy diagram is reduced. 

Acetoacetate is chemically unstable, and undergoes a non-enzymic reaction to yield acetone, which is only poorly metabolized. Most of it is excreted in the urine and in exhaled air — a waste of valuable metabolic fuel reserves in the fasting state. To avoid this, much of the acetoacetate is reduced to (3-hydroxybutyrate before being released from the liver. 

Ketone bodies Acetoacetate and 3-hydroxybutyrate (not chemically a ketone) formed in the liver from fatty acids in the fasting state and released into the circulation as metabolic fuels for use by other tissues. Acetone is also formed non-enzymically from acetoacetate. 

A. (The gas phase estimate is about 100 picoseconds for A at 1 atm pressure.) This suggests tliat tire great majority of fast bimolecular processes, e.g., ionic associations, acid-base reactions, metal complexations and ligand-enzyme binding reactions, as well as many slower reactions that are rate limited by a transition state barrier can be conveniently studied with fast transient metliods. 

In conclusion, the steady-state kinetics of mannitol phosphorylation catalyzed by II can be explained within the model shown in Fig. 8 which was based upon different types of experiments. Does this mean that the mechanisms of the R. sphaeroides II " and the E. coli II are different Probably not. First of all, kinetically the two models are only different in that the 11 " model is an extreme case of the II model. The reorientation of the binding site upon phosphorylation of the enzyme is infinitely fast and complete in the former model, whereas competition between the rate of reorientation of the site and the rate of substrate binding to the site gives rise to the two pathways in the latter model. The experimental set-up may not have been adequate to detect the second pathway in case of II " . The important differences between the two models are at the level of the molecular mechanisms. In the II " model, the orientation of the binding site is directly linked to the state of phosphorylation of the enzyme, whereas in the II" model, the state of phosphorylation of the enzyme modulates the activation energy of the isomerization of the binding site between the two sides of the membrane. Steady-state kinetics by itself can never exclusively discriminate between these different models at the molecular level since a condition may be proposed where these different models show similar kinetics. The II model is based upon many different types of data discussed in this chapter and the steady-state kinetics is shown to be merely consistent with the model. Therefore, the II model is more likely to be representative for the mechanisms of E-IIs. 

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