Enzymes pacemaker

Carbamoyl Phosphate Synthase I Is the Pacemaker Enzyme of the Urea Cycle... 

SLOW-BINDING INHIBITOR d-ALANINE-d-ALANINE LIGASE Slowest enzymic step in metabolic pathway, PACEMAKER ENZYME Slow partial exchange reactions,... 

Their antihypertensive efficacy is comparable to that of (3-adrenergic blockers and angiotensin-converting enzyme (ACE) inhibitors. The choice of a calcium channel blocker, especially for combination therapy, is largely influenced by the effect of the drug on cardiac pacemakers and contractility and coexisting diseases, such as angina, asthma, and peripheral vascular disease. 

Metabolic control can be understood to some extent by focusing attention on those enzymes that catalyze rate-limiting steps in a reaction sequence. Such pacemaker enzymes1-4 are often involved in reactions that determine the overall respiration rate of a cell, reactions that initiate major metabolic sequences, or reactions that initiate branch pathways in metabolism. Often the first step in a unique biosynthetic pathway for a compound acts as the pacemaker reaction. Such a reaction may be described as the committed step of the pathway. It usually proceeds with a large decrease in Gibbs energy and tends to be tightly controlled. Both the rate of synthesis of the enzyme protein and the activity of the enzyme, once it is formed, may be inhibited by feedback inhibition which occurs when an end product of a biosynthetic pathway accumulates... 

In spite of its usefulness, the pacemaker concept is oversimplified. It is often impossible to identify a specific pacemaker enzyme. When both catabolism and biosynthesis occur (e.g., as in the scheme in Fig. 11-2) it may be more useful to model the entire system with a computer than to try to identify pacemakers.7 8 It is also important to realize that reaction rates may be... 

The sensitivity coefficient can range from 1 for a pacemaker enzyme to almost zero for a very active enzyme that does not significantly limit the flux. The sum of Z1 to Zn is equal to 1 ... 

From this equation we see that for the flux to be sensitively dependent upon [P], both Z, and k must be reasonably large. This is exactly the case for many of the enzymes that have been identified as pacemakers. 

Nagaraj, V.J., Altenbach, D., Galati, V., Luscher, M., Meyer, A.D., Boiler, T., and Wiemken, A., Distinct regulation of sucrose sucrose-l-fructosyltransferase (1-SST) and sucrose fructan-6-fructosyltrans-ferase (6-SFT), the key enzymes of fructan synthesis in barley leaves 1-SST as the pacemaker, New Phytol., 161, 735-748, 2004. 

Bioelectrochemical generation of power by enzymes has also been considered. " " The usage of enzymes as catalysts in fuel cells has been vastly experimented, " and currently some enzymatic fuel cells are being used to produce electricity to power many number of electrical devices, like pumps, valves and pacemakers, or electronic devices, like radios, sensors, controllers, and processors. At present however, enzymatic fuel cells have been... 

Negative feedback inhibition is a process in which the product of a pathway inhibits the activity of the pacemaker enzyme. 

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