Common pathway

Reactions 33 and 35 constitute the two principal reactions of alkyl hydroperoxides with metal complexes and are the most common pathway for catalysis of LPOs (2). Both manganese and cobalt are especially effective in these reactions. There is extensive evidence that the oxidation of intermediate ketones is enhanced by a manganese catalyst, probably through an enol mechanism (34,96,183—185). 

FIGURE 15.5 The cascade of activation steps leading to blood clotting. The intrinsic and extrinsic pathways converge at Factor X, and the final common pathway involves the activation of thrombin and its conversion of fibrinogen into fibrin, which aggregates into ordered filamentous arrays that become cross-linked to form the clot. 

Although the Koenigs-Knorr reaction appears to involve a simple backside S 2 displacement of bromide ion by alkoxide ion, the situation is actually more complex. Both a and /3 anomers of tetraacetyl-o-glucopyranosyl bromide give the same /3-glycoside product, implying that they react by a common pathway. 

The citrate cycle is the final common pathway for the oxidation of acetyl-CoA derived from the metabolism of pyruvate, fatty acids, ketone bodies, and amino acids (Krebs, 1943 Greville, 1968). This is sometimes known as the Krebs or tricarboxylic acid cycle. Acetyl-CoA combines with oxaloacetate to form citrate which then undergoes a series of reactions involving the loss of two molecules of CO2 and four dehydrogenation steps. These reactions complete the cycle by regenerating oxaloacetate which can react with another molecule of acetyl-CoA (Figure 4). 

TOXIC RESPONSES THAT SHARE COMMON PATHWAYS OF EXPRESSION... 

The citric acid cycle is the final common pathway for the aerobic oxidation of carbohydrate, lipid, and protein because glucose, fatty acids, and most amino acids are metabolized to acetyl-CoA or intermediates of the cycle. It also has a central role in gluconeogenesis, lipogenesis, and interconversion of amino acids. Many of these processes occur in most tissues, but the hver is the only tissue in which all occur to a significant extent. The repercussions are therefore profound when, for example, large numbers of hepatic cells are damaged as in acute hepatitis or replaced by connective tissue (as in cirrhosis). Very few, if any, genetic abnormalities of citric acid cycle enzymes have been reported such ab-normahties would be incompatible with life or normal development. 

Initiation of the fibrin clot in response to tissue injury is carried out by the extrinsic pathway. How the intrinsic pathway is activated in vivo is unclear, but it involves a negatively charged surface. The intrinsic and extrinsic pathways converge in a final common path-vray involving the activation of prothrombin to thrombin and the thrombin-catalyzed cleavage of fibrinogen to form the fibrin clot. The intrinsic, extrinsic, and final common pathways are complex and involve many different proteins (Figure 51-1 and Table 51-1). In... 

Figure 51-1. The pathways of blood coagulation. The intrinsic and extrinsic pathways are indicated. The events depicted below factor Xa are designated the final common pathway, culminating in the formation of cross-linked fibrin. New observations (dotted arrow) include the finding that complexes of tissue factor and factor Vila activate not only factor X (in the classic extrinsic pathway) but also factor IX in the intrinsic pathway, in addition, thrombin and factor Xa feedback-activate at the two sites indicated (dashed arrows). (PK, prekallikrein HK, HMW kininogen PL, phospholipids.) (Reproduced, with permission, from Roberts HR, Lozier JN New perspectives on the coagulation cascade. Hosp Pract [Off Ed] 1992Jan 27 97.)...

The Final Common Pathway of Blood Clotting Involves Activation of Prothrombin to Thrombin... 

In the final common pathway, factor Xa, produced by either the intrinsic or the extrinsic pathway, activates prothrombin (factor II) to thrombin (factor Ila), which then converts fibrinogen to fibrin (Figure 51-1). 

The metabolism of phenols under anaerobic conditions has been examined under denitrifying, sulfate-reducing, Fe (lll)-reducing, and anaerobic nonmethanogenic conditions. It is plausible to suggest a common pathway that has been elucidated for denitrifying bacteria. This comprises (a) activation of phenol by the formation of phenylphosphate, (b) carboxylation at a position para to... 

SCHEME 10.2 Common pathways of QM formation in biological systems, (a) Stepwise two-electron oxidation by cytochrome P450 or a peroxidase, (b) Enzymatic oxidation of a catechol followed by spontaneous isomerization of the resulting n-quinone. (c) Enzymatic hydrolysis of a phosphate ester followed by base-catalyzed elimination of a leaving group from the benzylic position. 

Once the initial event occurs, secondary events occur at the cellular level that contribute to cell death. Regardless of the specific initiating event, the cellular processes that follow may be similar. Excitatory amino acids such as glutamate accumulate within the cells, causing intracellular calcium accumulation. Inflammation occurs and oxygen free radicals are formed ending in the common pathway of cell death. 

A number of factors can cause initial damage to the kidney. The resulting sequelae, however, follow a common pathway that promotes progression of CKD and results in irreversible damage leading to ESRD (Fig. 23-1). 

Inflammation is a common pathway in soft-tissue injury of musculoskeletal disorders. Inflammatory processes lead to two outcomes swelling and pain. Inflammatory processes... 

Activated partial thromboplastin time aPTT is performed by adding calcium phospholipids and kaolin to citrated blood and measures the time required for a fibrin clot to form. In this manner, aPTT measures the activity of intrinsic and common pathways. Prolongation of aPTT may be due to a deficiency or inhibitor for factors II, V, VIII, IX, X, XI, and XII. It also may be due to heparin, direct thrombin inhibitors, vitamin K deficiency, liver disease, or lupus anticoagulant. 

Lymphatic seeding is the most common pathway and frequently causes ascites. 

The alternative pathway may become activated by lipopolysaccharides, endotoxin (sepsis), virus, fungi, immunoglobulin A-antigen (IgA-Ag) immunocom-plexes, and foreign material. These activate C3, after which the common pathway of complement activation takes place (Fig. 4). There are also a number of inhibitors that regulate and control complement activation. The most important are the Cl-esterase inhibitor (Cl-Inh) and the membrane attack complex inhibitor factor (MACIF CD59). In sepsis a relative deficiency of Cl-Inh has been reported. Administration of Cl-Inh to patients with septic shock attenuates complement acti-... 

The axonal projections from the DDC-expressing cells in the ventral ganglion also show tendencies to follow common pathways. The projections from the ventral lateral serotonin cells extend medially to fuse with axons projecting from the contralateral serotonin cells. At the midline, this projection is met by an axonal projection from the medial dopamine cell. 

Over the years a number of general synthetic pathways to silenes have been developed these have been employed by research groups to generate families of silenes closely related in structure. It seems useful to list the most common pathways, together with references, in Table I14-91 and then to comment on some of them in detail. 

A common pathway has been tentatively put forward to account for both the arsenic and phosphorus reaction products (Scheme 20). Breaking of two bonds to one of the atoms in the P4 or As4 tetrahedron would lead... 

The first study was conducted to determine whether carotenoids and cholesterol share common pathways (transporters) for their intestinal absorption (During et al., 2005). Differentiated Caco-2 cells on membranes were incubated (16 h) with a carotenoid (1 pmol/L) with or without ezetimibe (EZ Zetia, an inhibitor of cholesterol transport), and with or without antibodies against the receptors, cluster determinant 36 (CD36) and scavenger receptor class B, type I (SR-BI). Carotenoid transport in Caco-2 cells (cellular uptake + secretion) was decreased by EZ (lOmg/L) as follows P-C and a-C (50% inhibition) P-cryptoxanthin and LYC (20%) LUT ZEA (1 1) (7%). EZ reduced cholesterol transport by 31%, but not retinol transport. P-Carotene transport was also inhibited by anti-SR-BI, but not by anti-CD36. The inhibitory effects of EZ and anti-SR-BI on P-C transport... 

Once the most interesting elements in e-waste appliances and the most common pathways of recycling them have been established, the content of the selected additives (Pb and PBDE) in these parts for computers and televisions is explained in more detail below. 

Verkhusha W, Chudakov DM, Gurskaya NG, Lukyanov S, Lukyanov KA (2004) Common pathway for the red chromophore formation in fluorescent proteins and chromoproteins. Chem Biol 11 845-854... 

Ford, L., Prasad, G.B.K.S., Wu, Y., Cross, H. and Taylor, M.J. (2000) Filarial Wolbachia HSP60 and LPS share common pathways in the activation of inflammatory responses. In First International Wolbachia Conference (Kolymbari, Crete, Greece, 7-12 June 2000), abstract book, pp. 125-126. 

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