Plenty signal

PFK is activated by AMP (the precursor for ADP and ATP) and by F26BP (which also acts as a positive allosteric effector ) but is inhibited by ATP, citrate and lowered pH ( end products of the pathway), ATP and citrate acting as negative allosteric effectors . In contrast FBPase is activated by citrate (a positive allosteric effector ) and inhibited by the plenty signal F26BP (a negative allosteric effector ). 

In these examples, precursors of the enzyme-catalysed reaction act as feed-forward inhibitors (AMP for PFK and citrate for FBPase). The plenty signal F26BP (elevated as a result of the precursor elevated blood glucose conditions) also activates PFK. Conversely, down the track , end products act as feedback inhibitors (ATP and citrate for PFK and F26BP - that can be loosely seen as an end product of blood glucose elevation by gluconeogenesis - for FBPase). 

Although, from a purely chemical point of view, learning how to create these complicated supramolecular structures has its own value, there are plenty of more practical reasons to investigate this chemistry. In the short term, these include catalysis and sensor applications, and in the long term, molecular electronics and molecular machines. With perhaps the exception of catalysis, all these applications will require some sort of signal transduction to allow for communication with the supramolecular device. This, of course, is one of the main reasons that electrochemistry is useful for supramolecular chemistry. Electron transfer provides a well-understood and very sensitive method to both communicate with supramolecular assemblies and control their structure.8... 

Citrate. PFK is also inhibited by citrate, the first product of the citric acid cycle proper (see Topic LI). A high level of citrate signals that there is a plentiful supply of citric acid cycle intermediates already and hence no additional breakdown of glucose via glycolysis is needed. 

The detector time constant is the response time of the detector to the signal passing through it. A slower time constant will result in less apparent noise, but it will compromise signal and also resolution for closely eluting peaks. For closely eluting peaks, therefore, it is important to use a faster time constant. If there is plenty of resolution, a slower time constant will provide a smoother baseline. The effect of the time constant is illustrated in Figure 8.6. 

Fatty acid synthesis and degradation are reciprocally regulated so that both are not simultaneously active. Acetyl CoA carboxylase, the essential control site, is phosphorylated and inactivated by AMP-dependent kinase. The phosphorylation is reversed by a protein phosphatase. Citrate, which signals an abundance of building blocks and energy, partly reverses the inhibition by phosphorylation. Carboxylase activity is stimulated by insulin and inhibited by glucagon and epinephrine. In times of plenty, fatty acyl CoAs do not enter the mitochondrial matrix, because malonyl CoA inhibits carnitine acyl transferase I. 

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