### A. Overview

Extracellular purines (adenosine, ADP, and ATP) and pyrimidines (UDP and UTP) are important signaling molecules that mediate diverse biological effects via cell-surface receptors termed purine receptors. In this review particular emphasis is placed on the discrepancy between the

/pdf/receptors-for-purines-and-pyrimidines-56f78tnpew.pdf

Receptors for Purines and Pyrimidines

The small (40S) subunit of eukaryotic ribosomes is believed to bind initially at the capped 5'-end of messenger RNA and then migrate, stopping at the first AUG codon in a favorable context for initiating translation. The first-AUG rule is not absolute, but there are rules for breaking the rule. Some anomalous observations that seemed to contradict the scanning mechanism now appear to be artifacts. A few genuine anomalies remain unexplained.

/pdf/the-scanning-model-for-translation-an-update-52r2in8l71.pdf

The scanning model for translation: an update.

GTPases are conserved molecular switches, built according to a common structural design. Rapidly accruing knowledge of individual GTPases--crystal structures, biochemical properties, or results of molecular genetic experiments--support and generate hypotheses relating structure to function in other members of the diverse family of GTPases.

The GTPase superfamily: conserved structure and molecular mechanism

The protective effects of estrogen on the cardiovascular system

Mechanical forces associated with blood flow play important roles in the acute control of vascular tone, the regulation of arterial structure and remodeling, and the localization of atherosclerotic lesions. Major regulation of the blood vessel responses occurs by the action of hemodynamic shear stresses on the endothelium. The transmission of hemodynamic forces throughout the endothelium and the mechanotransduction mechanisms that lead to biophysical, biochemical, and gene regulatory responses of endothelial cells to hemodynamic shear stresses are reviewed.

/pdf/flow-mediated-endothelial-mechanotransduction-281f54bq52.pdf

Flow-mediated endothelial mechanotransduction

Homologous or agonist-specific desensitization of beta-adrenergic receptors is thought to be mediated by a specific kinase, the beta-adrenergic receptor kinase (beta ARK). However, recent data suggest that a cofactor is required for this kinase to inhibit receptor function. The complementary DNA for such a cofactor was cloned and found to encode a 418-amino acid protein homologous to the retinal protein arrestin. The protein, termed beta-arrestin, was expressed and partially purified. It inhibited the signaling function of beta ARK-phosphorylated beta-adrenergic receptors by more than 75 percent, but not that of rhodopsin. It is proposed that beta-arrestin in concert with beta ARK effects homologous desensitization of beta-adrenergic receptors.

https://science.sciencemag.org/content/sci/248/4962/1547.full.pdf

Beta-arrestin: a protein that regulates beta-adrenergic receptor function

The current view of how steroid hormone receptors affect gene transcription is that these receptors, on binding ligand, change to a state in which they can interact with chromatin and regulate transcription of target genes. Receptor activation is believed to be dependent only on this ligand-binding event. Selected steroid hormone receptors can be activated in a ligand-independent manner by a membrane receptor agonist, the neurotransmitter dopamine. In vitro, dopamine faithfully mimicked the effect of progesterone by causing a translocation of chicken progesterone receptor (cPR) from cytoplasm to nucleus. Dual activation by progesterone and dopamine was dissociable, and a serine residue in the cPR was identified that is not necessary for progesterone-dependent activation of cPR, but is essential for dopamine activation of this receptor.

https://science.sciencemag.org/content/sci/254/5038/1636.full.pdf

Dopaminergic and ligand-independent activation of steroid hormone receptors.

A possible direct effect of guanine nucleotide binding (G) proteins on calcium channels was examined in membrane patches excised from guinea pig cardiac myocytes and bovine cardiac sarcolemmal vesicles incorporated into planar lipid bilayers. The guanosine triphosphate analog, GTP gamma S, prolonged the survival of excised calcium channels independently of the presence of adenosine 39,59-monophosphate (cAMP), adenosine triphosphate, cAMP-activated protein kinase, and the protein kinase C activator tetradecanoyl phorbol acetate. A specific G protein, activated Gs, or its alpha subunit, purified from the plasma membranes of human erythrocytes, prolonged the survival of excised channels and stimulated the activity of incorporated channels. Thus, in addition to regulating calcium channels indirectly through activation of cytoplasmic kinases, G proteins can regulate calcium channels directly. Since they also directly regulate a subset of potassium channels, G proteins are now known to directly gate two classes of membrane ion channels.

https://science.sciencemag.org/content/sci/238/4831/1288.full.pdf

A G protein directly regulates mammalian cardiac calcium channels.

The beta-adrenergic receptor kinase is an enzyme, possibly analogous to rhodopsin kinase, that multiply phosphorylates the beta-adrenergic receptor only when it is occupied by stimulatory agonists. Since this kinase may play an important role in mediating the process of homologous, or agonist-specific, desensitization, we investigated the functional consequences of receptor phosphorylation by the kinase and possible analogies with the mechanism of action of rhodopsin kinase. Pure hamster lung beta 2-adrenergic receptor, reconstituted in phospholipid vesicles, was assessed for its ability to mediate agonist-promoted stimulation of the GTPase activity of coreconstituted stimulatory guanine nucleotide-binding regulatory protein. When the receptor was phosphorylated by partially (approximately 350-fold) purified preparations of beta-adrenergic receptor kinase, as much as 80% inactivation of its functional activity was observed. However, the use of more highly purified enzyme preparations led to a dramatic decrease in the ability of phosphorylation to inactivate the receptor such that pure enzyme preparations (approximately 20,000-fold purified) caused only minimal (approximately 1off/- 7%) inactivation. Addition of pure retinal arrestin (48-kDa protein or S antigen), which is involved in enhancing the inactivating effect of rhodopsin phosphorylation by rhodopsin kinase, led to partial restoration of the functional effect of beta-adrenergic receptor kinase-promoted phosphorylation (41 +/- 3% inactivation). These results suggest the possibility that a protein analogous to retinal arrestin may exist in other tissues and function in concert with beta-adrenergic receptor kinase to regulate the activity of adenylate cyclase-coupled receptors.

https://www.pnas.org/content/pnas/84/24/8879.full.pdf

Functional desensitization of the isolated beta-adrenergic receptor by the beta-adrenergic receptor kinase: potential role of an analog of the retinal protein arrestin (48-kDa protein)

ATP-sensitive K+ (K+[ATP]) current is thought to be regulated by GTP-binding proteins (G proteins), but the pathways that couple receptor, G protein, and channel have not been defined. We studied r...

Juan Codina

Papers

Beta-arrestin: a protein that regulates beta-adrenergic receptor function

Dopaminergic and ligand-independent activation of steroid hormone receptors.

A G protein directly regulates mammalian cardiac calcium channels.

Functional desensitization of the isolated beta-adrenergic receptor by the beta-adrenergic receptor kinase: potential role of an analog of the retinal protein arrestin (48-kDa protein)

Coupling of ATP-sensitive K+ channels to A1 receptors by G proteins in rat ventricular myocytes.