Cell surface receptors activation

Figure 2. Mechanism of PDH. The three different subunits of the PDH complex in the mitochondrial matrix (E, pyruvate decarboxylase E2, dihydrolipoamide acyltrans-ferase Ej, dihydrolipoamide dehydrogenase) catalyze the oxidative decarboxylation of pyruvate to acetyl-CoA and CO2. E, decarboxylates pyruvate and transfers the acetyl-group to lipoamide. Lipoamide is linked to the group of a lysine residue to E2 to form a flexible chain which rotates between the active sites of E, E2, and E3. E2 then transfers the acetyl-group from lipoamide to CoASH leaving the lipoamide in the reduced form. This in turn is oxidized by E3, which is an NAD-dependent (low potential) flavoprotein, completing the catalytic cycle. PDH activity is controlled in two ways by product inhibition by NADH and acetyl-CoA formed from pyruvate (or by P-oxidation), and by inactivation by phosphorylation of Ej by a specific ATP-de-pendent protein kinase associated with the complex, or activation by dephosphorylation by a specific phosphoprotein phosphatase. The phosphatase is activated by increases in the concentration of Ca in the matrix. The combination of insulin with its cell surface receptor activates PDH by activating the phosphatase by an unknown mechanism.

Figure 14-8. Overview of pathways that regulate programmed cell death. Apoptosis may occur in response to signaling through either the extrinsic pathway or the intrinsic pathway. In each case, proteolytic cleavage activates an initiator caspase, caspase 8 or 9, either of which can cleave an effector caspase such as caspase 3. Apaf-1 is part of a large complex called the apoptosome that mediates the intrinsic pathway. Binding of an extracellular death ligand to its cell-surface receptor activates the extrinsic pathway.

Accomplishments of aptamers targeting cell surface receptor activity and intracellular targets... 

Fig. 5 Schematic representation of the surface modification steps used by Ganger et al. to produce a biologically active surface in a microreactor. Biotin-labeled human anti- 5-integrin (HAI) was bound to modified PDMS and used to study cell surface receptor activity. (From Ref.. ) (View this art in color at www.dekker.com.)...

Hormones that bind to cell-surface receptors activate or form a complex with a transducer protein in the membrane that will cause the activation of some enzymatic activity in the cytoplasm of the cell, prodncing a second messenger. 

Figure 49-1. The sequence of events leading to the release of cortisol from the adrenal gland. Binding of ACTH to cell surface receptors activates adenylate cyclase to produce cAMP, which in turn activates protein kinase A. This causes phosphorylation events to occur that cause cholesterol to be released from cholesterol ester droplets in the cell. This initiates the conversion of cholesterol to cortisol, which is then released into the bloodstream.

The steroid hormone 1,25-dihydroxy vitamin D3 (calcitriol) slowly increases both intestinal calcium absorption and bone resorption, and is also stimulated through low calcium levels. In contrast, calcitonin rapidly inhibits osteoclast activity and thus decreases serum calcium levels. Calcitonin is secreted by the clear cells of the thyroid and inhibits osteoclast activity by increasing the intracellular cyclic AMP content via binding to a specific cell surface receptor, thus causing a contraction of the resorbing cell membrane. The biological relevance of calcitonin in human calcium homeostasis is not well established. 

Muscarinic acetylcholine receptors (mAChRs) form a class of cell surface receptors that are activated upon binding of the neurotransmitter, acetylcholine. Structurally and functionally, mAChRs are prototypical members of the superfamily of G protein-coupled receptors. Following acetylcholine binding, the activated mAChRs interact with distinct classes of heterotrimeric G proteins resulting in the activation or inhibition of distinct downstream signaling cascades. 

The neurotransmitter acetylcholine (ACh) exerts its diverse pharmacological actions via binding to and subsequent activation of two general classes of cell surface receptors, the nicotinic and the mAChRs. These two classes of ACh receptors have distinct structural and functional properties. The nicotinic receptors,... 

Real-time spectroscopic methods can be used to measure the binding, dissociation, and internalization of fluorescent ligands with cell-surface receptors on cells and membranes. The time resolution available in these methods is sufficient to permit a detailed analysis of complex processes involved in cell activation, particularly receptor-G protein dynamics. A description of the kinetics and thermodynamics of these processes will contribute to our understanding of the basis of stimulus potency and efficacy. 

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