Controlled metabolism

Proteins embedded in the shell of lipoproteins. They serve as scaffold for assembly of the lipoprotein particle in the endoplasmic reticulum. In addition, they control metabolism of lipoproteins in the circulation by interaction with enzymes such as lipases. Finally, apolipoproteins determine cellular uptake of the particles by interaction with specific lipoprotein receptors expressed on the surface of target cells. 

C. S. Chin, V. Chubukov, E. R. Jolly, J. DeRisi, and H. Li, Dynamics and design principles of a basic regulatory architecture controlling metabolic pathways. PLoS Biol. 6(6), el46 (2008). 

Hypothalamus Controls metabolism, sleep, eating, and drinking... 

Both represent strategies to control metabolism. The action of protein kinases is reversed by protein phosphatases (Figure 1-9-1). 

Enzyme inhibitors are chemicals that may serve as a natural means of controlling metabolic activity by reducing the number of enzyme molecules available for catalysis. In many cases, natural or synthetic inhibitors have allowed us to unravel the pathways and mechanisms of intermediary metabolism. Enzyme inhibitors may also be used as pesticides or drugs. Such materials are designed so that they inhibit a specific enzyme that is peculiar to an organism or a disease state. For example, a good antibiotic may inhibit a bacterial enzyme, but it should have no effect on the host person or animal. 

In the cell, the free Ca concentration is subject to strict regulation, and targeted increase of Ca concentration is a universal means of controlling metabolic reactions. Several processes are involved in its regulation (Fig. 6.6) release from Ca storage, Ca influx from the extracellular space and transport back into the Ca storage. 

A large number of proteins present in the outer surfaces of cells serve as receptors that receive chemical messages and other signals from outside the cell. The receptors, which are sometimes enzymes, respond by generating internal signals that control metabolism and cell growth. Such molecular signaling is another major area of contemporary biochemistry. 

A Few Covalent Modification Reactions Utilized to Control Metabolism... 

Adipokinetic hormones control metabolism of insects during long-distance flight.359 363 In the migratory locust these hormones consist of a pair of related octapeptides and a decapeptide (Table 30-5). The hormones stimulate triacylglycerol lipase in the insects fat bodies, induce release of carbohydrates from body stores, and affect many other aspects of metabolism.363 Insects also have hormones of the insulin family, proteins consisting of disulfide-linked A and B chains as in insulin. The silkworm Bombyx mori has 38 genes for the insulinlike bombyxins, which are synthesized in the brain.364... 

OPERON A tightly linked (i.e., contiguous) set of related genes and regulatory sites, by which a given genetically controlled metabolic activity is regulated. 

Studies In Dr. Greger s laboratory also have evaluated the Influence of tin or zinc retention In humans (61). Eight healthy male volunteers received their accustomed caloric Intakes, 3150 to 3700 kcal, as controlled, metabolic diets of real foodstuffs for two consecutive 20-day cycles two balance periods — comprising days 7-12 and days 13-18 of each cycle — were undertaken. The diets contained an average of 13.5 mg of zinc dally. In a randomized fashion, the rations during one of the dietary cycles had 50 mg of Sn as stannous chloride added. The dietary Sn/Zn... 

A later single-dose study in eight patients with moderate to severe cirrhosis and a PT of 2-5 seconds above the npper limit of normal, showed an approximate doubling of the half-life compared to controls. Metabolic inversion of the inactive R-ibuprofen to the active S-ibupro-fen may also be impaired in hepatic cirrhosis, because the AUC ratio of R- to S-ibuprofen was significantly higher in patients with cirrhosis. Medicinal ibuprofen is supplied as a racemic mixture [39]. 

The most recently identified class of transcription attenuation mechanism involves direct sensing of the effector molecule by the nascent transcript (52-54). These RNA sensors control metabolically diverse pathways. As for the other attenuation and antitermination mechaiusms discussed thus far, recognition of the particular effector molecule occurs with the appropriate affinity and high specificity required for precise control of gene expression. 

The intricate network of biochemical reactions occurring within the restricted volume of the liver cell requires subtly controlled metabolic regulatory mechanisms. (28) These occur on four levels (7.) at the molecular level, (2.) within the organelles, (3.) at the cellular level, and (4.) at the organ level. 

Fig. 12.4 An Overview of mRNA Biosynthesis Synthesis and Destruction of RNA is used to control metabolism in cells...

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