Intracellular reactions

Solutions of weak acids or bases and their conjugates exhibit buffering, the abihty to resist a change in pH following addition of strong acid or base. Since many metabohc reactions are accompanied by the release or uptake of protons, most intracellular reactions are buffered. Oxidative metabohsm produces CO2, the anhydride of carbonic acid, which if not buffered would produce severe acidosis. Maintenance of a constant pH involves buffering by phosphate, bicarbonate, and proteins, which accept or release protons to resist a change... 

A. Levina, L. Zhang, and P. A. Lay, Formation and reactivity of chromium (V). Thiolato complexes A model for the intracellular reactions of carcinogenic chromium(VI) with biological thiols, /. Am. Chem. Soc., 132 (2010) 8720-8731. 

It plays a vital role in various intracellular reactions e.g. conversion of serine to glycine, synthesis of thymidylate, synthesis of purines, histidine metabolism etc. Due to folic acid deficiency these reactions are affected. 

Fig. 3.8. Variability of receptor systems and signal pathways, a) For one receptor of a given binding specificity (binding to hormone H) there can be different snbtypes in the same ceU (Rl, R2) or in other cell types (Rl )- b) The hormone H can induce different reactions (X, X ) upon binding the different receptor types (Rl, R2). The receptor types Rl and R2 can be found simultaneous in one cell, c) the binding of two different hormones (H, H ) to different receptors (Rl , R3) can induce the same intracellular reaction. The characteristics a) and b) contribute to a high degree to the diversity and variability of hormonal signal transduction. Point c) illustrates the principle that important cellular metabolites or reactions can be controlled by different signal transduction pathways.

A severe mechanical wound on a single leaf of tomato plants initiates a complex series of extracellular and intracellular reactions which result in the synthesis and accumulation of two proteinase Inhibitors, Inhibitors I and II, in leaf cells (J, 2. A second wounding, within a few hours, results in a 2-3 fold Increase in the rates of accumulation initiated by the... 

The Intracellular Reactions of Nitric Oxide in the Immune System and Its Enzymatic Synthesis... 

II. INTRACELLULAR REACTIONS OF NITRIC OXIDE IN THE IMMUNE SYSTEM... 

The other thiosemicarbazones are less well studied and as yet the link between antiviral action and chelation is not fully established. It has been proposed that the chelation of iron(II), a cofactor of ribonucleoside diphosphate reductase, could be the principal mode of action of the thiosemicarbazones300. However, other mechanisms are possible. Investigations of the ESR spectra of copper(II) complexes of thiosemicarbazones has been used to follow the intracellular reactions of the complexes - see Antholine et al.301 for a review. In Ehrlich cells the chelate becomes localized in the cell membrane302. This spectroscopic technique could also be used to monitor the antimala-rial action of 2-acetylpyridine thiosemicarbazones303. ... 

DOM participates in several reactions that occur in the extracellular environment. In contrast to intracellular reactions, environmental reactions are more or less nonspecific (excepting some enzymatic reactions), unregulated, and opportunistic. For heuristic purposes, these reactions can grouped into three categories hydrolytic, redox, and associative. 

The majority of processes occurring in the condensed phase are characterized by intracellular reactions involving the primary products of the transformation. This impedes the isolation of particular elementary steps from the overall process. These difficulties do not arise for an intermediate stabilized on the solid surface. The low-molecular products of the reactions involving this intermediate (atoms, radicals, or molecules) the zone of transformation through the gas phase can leave without hindrance. The occurrence of intracellular reactions is virtually ruled out, which makes it possible to detect primary steps of the corresponding processes. 

After administration, the drug circulates in the blood, primarily as the chloride (for cisplatin), or as another rather inert form (such as the biscar-boxylate in carboplatin). In the blood, also reactions with proteins and rescue agents can take place. Upon passing through cell walls (either actively or passively), intracellular reactions with peptides and proteins may take place, presumably followed by transfer to nucleic acids. Given the strong (kinetic) preference of Pt compounds to react with class-B donor atoms (such as those from thiolates and thioethers), binding to nucleic-acid bases (a thermodynamic end product) must at least occur partially via labile intermediates. 

The studies reported here using the isolated, vascularly perfused rat intestine system and isolated brush border membrane vesicles fail to support a role for a specific zinc-binding ligand involved in zinc uptake in the rat. Rather, the extent of zinc uptake involves the interaction of several phenomena, including both extracellular and intracellular reactions. It appears that the major pathway of zinc uptake under normal dietary conditions involves the transfer of zinc from various dietary components to a carrier mediated transport system at the brush border membrane. The net absorption of zinc from the lumen could involve a competition between various dietary components, zinc binding ligands and the membrane carrier for zinc. Thus, in some cases, those compounds in the lumen with a higher affinity for zinc than the membrane component will be less likely to permit transfer of zinc to the carrier, while compounds with a lower affinity for zinc will increase the amount of zinc made... 

Micro-organisms are inactivated when metabolically irreversible deleterious intracellular reactions occur. At high temperatures and in the presence of moisture, as in steam sterilization, the energy input from the steam inactivates micro-organisms by denaturation of intracellular proteins. 

The major classes of structurally altered amino-acid side-chains within ribosomally synthesised polypeptides, which are achieved by intracellular reactions, are listed in Table 1.2 (see also Chapter 8). 

The relative content of the dietary fat components varies with different sources but generally the physico-chemical properties are rather similar. For absorption to take place the physico-chemical properties of the fat have to be changed. This takes place as a consequence of the lipolytic activity in the intestinal tract and the addition of bile to chyme. Through lipolytic enzymes the dietary lipids are converted to more polar products. Bile contributes bile salt-phospholipid-cholesterol aggregates to the intestinal content (cf. Chapter 13). The concerted action of these agents is the formation of lipid products in a physical state which allows them to be transported into the enterocyte membrane and onwards for further metabolism in the cell. Bile salts are involved in the proper function of some of these enzymatic reactions and in the formation of product phases on which a normal uptake process is based. Little is known at present of the importance of bile salts for the intracellular reactions following uptake of fat into the enterocyte. Different aspects of intestinal lipid absorption have been reviewed in recent years by Patton [7], Thomson and Dietschy [8], Carey [9], Carey et al. [10], Wells and Direnzo [11], and Grundy [12]. The role of bile acids in fat absorption has been discussed by Holt [13]. 

Neirinckx RD, Burke JF, Harrison RC, Forster AM, Andersen AR, Lassen NA (1988) The retention mechanism of technetium-99m-HMPAO intracellular reaction with glutathione. J Cereb Blood Flow Metab 8(Suppl 1) S4-S12... 

Fig. 2. Schematic structure of cell receptors and levels of complexity in receptor signaling. Bound receptors may initiate a cascade of intracellular reactions that lead to short-and/or long-term responses.

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