Incorporation into cells

Metabolites may be incorporated into cell structures rapidly. 

Perhaps the most difficult inherent problem in metal remediation is that metals, although they may be released in the breakdown of a metal-containing compound, are not degradable in the same sense as carbon-based molecules. The metal atom is not the major building block for new cellular components, and while a significant amount of carbon is released to the atmosphere as C02, the metal atom is often not volatilized. Both incorporation into cell mass and volatilization facilitate carbon removal from environmental systems. In contrast, metals, unless removed completely from a system through intervention, will persist indefinitely. 

Vitamin B1 is required in humans for two essential enzymatic reactions Ihe synthesis of methionine and the isomerization of methylmalonyl CcA that is produced during the degradation of some amino acids, and fatly acids with odd numbers of carbon atoms (Figure 28.5). When the vitamin is deficient, abnormal fatty acids accumulate and become incorporated into cell membranes, including those of the nervous system. This may account for some of the neurologic manifestations of vitamin P12 deficiency. 

The opposite sequence, reduction of nitrate and nitrite ions, provides a major route of acquisition of ammonia for incorporation into cells by bacteria, fungi, and green plants (Fig. 24-1). Assimilatory (biosynthetic) nitrate reductases catalyze the two-electron reduction of nitrate to nitrite (Eq. 16-61). This is thought to occur at the molybdenum atom of the large 900-residue highly regulated793 molybdopterin-dependent enzyme. In green plants the reductant is... 

The main portion of the input of organic material into the sediment is particulate organic carbon which has to be enzymatically decomposed, at least partly, prior to incorporation into cells. In this process, extracellular enzymes are involved which are secreted by living cells (Corpe and Winters, 1972) or liberated during the lysis of dead and decaying cells. As shown by Burns (1980) some of these enzymes may retain their activity outside the cells by the formation of humic-enzyme complexes bound to clay particles. 

Ischemia also increased the BrdU incorporation into cells of blood vessel walls, and a vascular origin for at least some of the progenitor cells in DG could be deducted as reported previously (Yamashima et al. 2004). 

Certain fatty acids in the diet could be incorporated into cell membranes, possibly producing changes in cell behavior that are associated with promotion. 

Figure 7. Change in intracellular pH induced by oxidant addition to HeLa cells. Internal pH measured by change in fluorescence of BCECF incorporated into cells. Modified from Toole-Simms (1988).

Costonis et al. (33) were unable to demonstrate a positive correlation between ambient sulfur dioxide levels and inorganic sulfur ion accumulation in the needles of pines which are injured by relatively low levels of sulfur dioxide in the air. White pines growing in air polluted with more than 0.25 ppm of sulfur dioxide are often stunted, and a direct correlation can be obtained between plant growth and ambient S02 levels (34). However, tissue analysis does not reveal a measurable rise in sulfur level as inorganic sulfate ions. It is posible that the excess sulfur is incorporated into cell protein, but the data conflict (28, 35). For these reasons, it is not possible to follow sulfur accumulation in plants chronically exposed to low levels of ambient S02 without resorting to labeled S02. 

Because the enzyme functions as a catalyst, its inhibition or inactivation may decrease the rate of a particular metabolic reaction. The reduction in the rate of this reaction may inhibit the pathway in which this reaction occurs and, in turn, result in the depletion of a product or the accumulation of precursors or intermediates. Changes in 02 or C02 exchange, pools of various metabolites, and the metabolism of glucose (both catabolism and incorporation into cell wall polysaccharides) that have been observed also support this hypothesis. 

Hydrogen Movement within the Cell, and Incorporation into Cell Components... 

In a plant, nitrite reductase catalyses reduction of its substrate to ammonia, which is subsequently incorporated into cell material. This type of nitrite reductase is classified as an assimilatory enzyme. The plant enzyme is found in the chloroplasts and acquires reductant from ferredoxin which is in turn reduced by the action of the photosystems that derive electrons... 

Much like metal recovery from dilute streams, the use of three-dimensional electrodes will enhance the oxidation rates of low-concentration organics by increasing the surface area available for reaction. Moreover, porous electrodes which could be incorporated into cells using solid electrolytes can draw upon technologies developed for other electrochemical systems such as PEM-based water electrolyzers and fuel cells. 

The nanoparticles can be incorporated into cells by incubation the nanoparticies suspended in DMEM medium with the cells for 12 to 48 hours. From dark field light scattering imaging [54], it has been established that gold nanoparticies are taken intracellulariy into these cell lines. The nanoparticies are accumulated inside cytoplasm of live cells by receptor-mediated endocytosis processes. Figure 20.16 shows that for most of samples gold nanospheres quench the protein fluorescoice at 12 h incubation time. However, in some samples fluorescence enhancement is observed. 

Premkumar DR, Fukuoka Y, Sevlever D, Brunschwig E, Rosen-berry TL, Tykocinski ML, Medof ME. Properties of exogenously added GPI-anchored proteins following their incorporation into cells. J. Cell. Biochem. 2001 82 234-245. 

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