Metabolic processes, regulation

In humans, most steroids function as hormones, chemical messengers that are secreted by endocrine glands and carried through the bloodstream to target tissues. There are two main classes of steroid hormones the sex hormones, which control maturation, tissue growth, and reproduction, and the adrenocortical hormones, which regulate a variety of metabolic processes. 

Phosphonate analogs to phosphate esters, in which the P—0 bond is formally replaced by a P—C bond, have attracted attention due to their stability toward the hydrolytic action of phosphatases, which renders them potential inhibitors or regulators of metabolic processes. Two alternative pathways, in fact, may achieve introduction of the phosphonate moiety by enzyme catalysis. The first employs the bioisosteric methylene phosphonate analog (39), which yields products related to sugar 1-phosphates such as (71)/(72) (Figure 10.28) [102,107]. This strategy is rather effective because of the inherent stability of (39) as a replacement for (25), but depends on the individual tolerance of the aldolase for structural modification close... 

Many of these compounds—puromycin and cycloheximide in particular—are not cfinically useful but have been important in elucidating the role of protein synthesis in the regulation of metabolic processes, particularly enzyme induction by hormones. 

Regulates metabolic processes through secretion of hormones... 

As argued in the previous sections, cellular metabolism is a highly dynamic process, and a description entirely in terms of flux balance constraints is clearly not sufficient to understand and predict the functioning of metabolic processes [334, 335], Specifically, we seek to demonstrate that the dynamic properties of large-scale metabolic networks play a far more important role than currently anticipated. Understanding the dynamics of metabolic networks will prove critical to a further understanding of metabolic function and regulation and critical to our ability to manipulate cellular system in a desired way. 

A calpain inhibitor, the DPK of N-dimethyltyrosine, was isolated from Streptomyces griseus and this compound showed activity in the calpain assay as described by Alvarez etal Calpain is a cytosolic protease regulated by calcium and is distributed in mammalian and avian cells. Calpain catalyzes proteolysis of target protein in cells, causing changes in metabolic processes such as the activation of protein kinase C, neuropeptide metabolism, and the activation of platelets. It is proposed that these inhibitors can be used in the treatment of neurodegen-erative diseases. 

Macroelements, as well as basic elements are essential for plant and animal organisms. They are the building materials that support tissue, teeth, skin, and hair, play an important role in water-electrolyte management and pH regulation, and are parts of many active compounds vital for metabolic processes. 

The purine and pyrimidine bases play an important role in the metabolic processes of cells through their involvement in the regulation of protein synthesis. Thus, several synthetic analogues of these compounds are used to interrupt the cancer cell growth. One such example is an adenine mimic, 6-mercaptopurine, which is a well known anticancer drug. 

In Chapters 13 through 22 we have discussed metabolism at the level of the individual cell, emphasizing central pathways common to almost all cells, prokaryotic and eukaryotic. We have seen how metabolic processes within cells are regulated at the level of individual enzyme reactions, by substrate availability, by allosteric mechanisms, and by phosphorylation or other covalent modifications of enzymes. 

The regulation of the reaction velocity of enzymes is essential if an organ ism is to coordinate its numerous metabolic processes. The rates of most enzymes are responsive to changes in substrate concentration, because the intracellular level of many substrates is in the range of the Km. Thus, an increase in substrate concentration prompts an increase in reaction rate, which tends to return the concentration of substrate toward normal. In addition, some enzymes with specialized regulatory functions respond to allosteric effectors or covalent modification, or they show altered rates of enzyme synthesis when physiologic conditions are changed. 

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