Metabolic pathways storage

After reuptake into the cytosol, some noradrenaline may be taken up into the storage vesicles by the vesicular transporter and stored in the vesicles for subsequent release (see above). However, it is thought that the majority is broken down within the cytosol of the nerve terminal by monoamine oxidase (MAO ECl.4.3.4). A second degradative enzyme, catechol-O-methyl transferase (COMT EC2.1.1.6), is found mostly in nonneuronal tissues, such as smooth muscle, endothelial cells or glia. The metabolic pathway for noradrenaline follows a complex sequence of alternatives because the metabolic product of each of these enzymes can act as a substrate for the other (Fig 8.8). This could enable one of these enzymes to compensate for a deficiency in the other to some extent. 

Insulin also plays a role in fat metabolism. In humans, most fatty acid synthesis takes place in the liver. The mechanism of action of insulin involves directing excess nutrient molecules toward metabolic pathways leading to fat synthesis. These fatty acids are then transported to storage sites, predominantly adipose tissue. Finally, insulin stimulates the uptake of amino acids into cells where they are incorporated into proteins. 

Figure 1. Different histone chaperones in the key histone metabolic pathways Functions of histone chaperones range from the storage of newly synthesized histones in the cytoplasm, its transfer into the nucleus and in histone assembly into nucleosomes. Apart from diis die histone chaperones are also involved in histone exchange, maintenance of heterochromatin and in the regulation of chromatin structure during transcription. (See Colour Plate 10.)...

Histamine metabolism differs from that of classical neurotransmitters because histamine is so widely distributed in the body. The highest concentrations in human tissues are found in the lung, stomach, and skin (upto 33 ug/g tissue). Histamine metabolic pathways are simple histamine is produced from histidine in just one step (see figure 4.11). The principal production takes place in the mast cells of the peritoneal cavity and connective tissues. The gastric mucosa is another major storage tissue. Histamine can be found in the brain as well. 

However, very low plasma levels of HDL cholesterol are also found in patients with genetically disturbed metabolic pathways that are indirectly linked to HDL metabolism. For example, many patients with lipid storage diseases like Gaucher s disease (glucocerobrosidase deficiency, OMIM 230800-231000), Nieman-Pick disease types A or (sphingomyelinase deficiency, OMIM 257200 and 607616, respectively), Niemann-Pick disease type C (OMIM 257220), hypertriglyceridemia, or diabetes mellitus present with low HDL cholesterol [22]. 

Lindane is absorbed from the gastrointestinal tract, the respiratory tract, and skin. The metabolism of lindane is complex and involves a number of pathways depending on which isomer of hexachlorocyclohexane (HCH) is involved (lindane is the gamma (y) isomer). It is nonetheless rapid. Lindane is metabolized in the liver by microsomal enzymes. The main pathways include stepwise elimination of chlorines to form tri- and tetrachloro-phenols and conjugation with sulfates or glucuron-ides and subsequent elimination. Other metabolic pathways involve the production of mercaptura-tes. These water-soluble products are eliminated in the urine. Lindane is bound by serum proteins in the blood. Storage is in adipose tissue and other... 

The physiological functions of hormones have been broadly categorized into those that (1) affect growth and development, (2) exert homeostatic control of metabolic pathways, and (3) regulate the production, use, and storage of energy. The descriptions below illustrate examples of these functions and mechanisms of control of hormone secretion. 

Distribution, Storage and Excretion. Hydrocarbons in each of the aliphatic and aromatic fractions are expected to be distributed throughout tissues and organs following absorption. Preferential distribution to fatty tissues occurs especially with aliphatic hydrocarbons. Ingested or inhaled volatile aliphatic and aromatic hydrocarbons in the HC5-EC8 and EC5-EC9 fractions can be eliminated in exhaled breath as unchanged parent compound. Metabolic elimination of aromatic hydrocarbons in each EC fraction predominately occurs via oxidative metabolic pathways involving... 

Fig. n.2 Schematic model forthe main signaling and metabolic pathways coupling hormonal stimuli and NEFA to (regulated) TAG synthesis, storage and mobilization in adipo-... 

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