The Concise Guide to PHARMACOLOGY 2019/20 is the fourth in this series of biennial publications. The Concise Guide provides concise overviews of the key properties of nearly 1800 human drug targets with an emphasis on selective pharmacology (where available), plus links to the open access knowledgebase source of drug targets and their ligands (http://www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. Although the Concise Guide represents approximately 400 pages, the material presented is substantially reduced compared to information and links presented on the website. It provides a permanent, citable, point‐in‐time record that will survive database updates. The full contents of this section can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.14752. Enzymes are one of the six major pharmacological targets into which the Guide is divided, with the others being: G protein‐coupled receptors, ion channels, nuclear hormone receptors, catalytic receptors and transporters. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. The landscape format of the Concise Guide is designed to facilitate comparison of related targets from material contemporary to mid‐2019, and supersedes data presented in the 2017/18, 2015/16 and 2013/14 Concise Guides and previous Guides to Receptors and Channels. It is produced in close conjunction with the International Union of Basic and Clinical Pharmacology Committee on Receptor Nomenclature and Drug Classification (NC‐IUPHAR), therefore, providing official IUPHAR classification and nomenclature for human drug targets, where appropriate.

Abstract-In this review, we outline the current knowledge on the regulation of nitric oxide (NO)-sensitive guanylyl cyclase (GC). Besides NO, the physiological activator that binds to the prosthetic heme group of the enzyme, two novel classes of GC activators have been identified that may have broad pharmacological implications. YC-1 and YC-1-like substances act as NO sensitizers, whereas the substance BAY 58-2667 stimulates NO-sensitive GC NO-independently and preferentially activates the heme-free form of the enzyme. Sensitization and desensitization of NO/cGMP signaling have been reported to occur on the level of NO-sensitive GC; in the present study, an alternative mechanism is introduced explaining the adaptation of the NO-induced cGMP response by a long-term activation of the cGMPdegrading phosphodiesterase 5 (PDE5

It took at least a decade to realize that the toxic gas NO is the physiological activator of soluble guanylyl cyclase (sGC), thereby acting as a signaling molecule in the nervous and cardiovascular systems. Despite its rather poor sGC‐activating property, CO has also been implicated as a physiological stimulator of sGC in neurotransmission and vasorelaxation. Here, we establish YC‐1 as a novel NO‐independent sGC activator that potentiates both CO‐ and NO‐induced sGC stimulation. As this potentiating effect is also observed with protoporphyrin IX which activates sGC independently of a gaseous ligand, we conclude that stabilization of the enzyme's active configuration is the underlying mechanism of YC‐1′s action. Moreover, the results obtained with YC‐1 reveal that CO is capable of stimulating sGC to a degree similar to NO, and thus provide the molecular basis for CO functioning as a signaling molecule.

1 Carbon monoxide (CO), one of the end products of heme catabolism by heme oxygenase, possesses antihypertensive and vasodilatory characteristics. We have recently discovered that certain transition metal carbonyls are capable of releasing CO in biological fluids and modulate physiological functions via the delivery of CO. Because the initial compounds identified were not water soluble, we have synthesized new CO-releasing molecules that are chemically modified to allow solubility in water. The aim of this study was to assess the vasoactive properties of tricarbonylchloro(glycinato)ruthenium(II) (CORM-3) in vitro and in vivo. 2 CORM-3 produced a concentration-dependent relaxation in vessels precontracted with phenylephrine, exerting significant vasodilatation starting at concentrations of 25-50 mM. Inactive CORM-3, which does not release CO, did not affect vascular tone. 3 Blockers of ATP-dependent potassium channels (glibenclamide) or guanylate cyclase activity (ODQ) considerably reduced CORM-3-dependent relaxation, confirming that potassium channels activation and cGMP partly mediate the vasoactive properties of CO. In fact, increased levels of cGMP were detected in aortas following CORM-3 stimulation. 4 The in vitro and in vivo vasorelaxant activities of CORM-3 were further enhanced in the presence of YC-1, a benzylindazole derivative which is known to sensitize guanylate cyclase to activation by CO. Interestingly, inhibiting nitric oxide production or removing the endothelium significantly decreased vasodilatation by CORM-3, suggesting that factors produced by the endothelium influence CORM-3 vascular activities. 5 These results, together with our previous findings on the cardioprotective functions of CORM-3, indicate that this molecule is an excellent prototype of water-soluble CO carriers for studying the pharmacological and biological features of CO.

The signaling molecule nitric oxide (NO), first described as endothelium-derived relaxing factor (EDRF), acts as physiological activator of NO-sensitive guanylyl cyclase (NO-GC) in the cardiovascular, gastrointestinal, and nervous systems. Besides NO-GC, other NO targets have been proposed; however, their particular contribution still remains unclear. Here, we generated mice deficient for the ␤1 subunit of NO-GC, which resulted in complete loss of the enzyme. GC-KO mice have a life span of 3-4 weeks but then die because of intestinal dysmotility; however, they can be rescued by feeding them a fiber-free diet. Apparently, NO-GC is absolutely vital for the maintenance of normal peristalsis of the gut. GC-KO mice show a pronounced increase in blood pressure, underlining the importance of NO in the regulation of smooth muscle tone in vivo. The lack of an NO effect on aortic relaxation and platelet aggregation confirms NO-GC as the only NO target regulating these two functions, excluding cGMP-independent mechanisms. Our knockout model completely disrupts the NO/cGMP signaling cascade and provides evidence for the unique role of NO-GC as NO receptor.cardiovascular ͉ knockout mice ͉ cGMP ͉ platelet aggregation ͉ smooth muscle relaxation T he nitric oxide (NO)/cGMP signaling cascade regulates a plethora of physiological functions in the cardiovascular, neuronal, and gastrointestinal systems (1-3). In the vascular system, NO, first recognized as endothelium-derived relaxing factor (EDRF; ref. 4), has been shown to mediate smooth muscle relaxation and inhibition of platelet aggregation. NO is synthesized by the family of NO synthases which exist in endothelial, neuronal, and inducible forms. The prominent receptor known to date is the enzyme NO-sensitive guanylyl cyclase (NO-GC). Stimulation of NO-GC by NO results in the production of the second messenger, cGMP, which exerts its effects via cGMPdependent kinases, channels, or phosphodiesterases (5-8). Besides these cGMP-mediated effects, NO is thought to mediate a variety of effects via cGMP-independent mechanisms in the cardiovascular system (for a review, see ref. 9).To gain further insight into the NO/cGMP signaling cascade, mice deficient in NO synthases (NOS) have been generated (10)(11)(12)(13)(14). Although these mouse lines have tremendously helped to understand NO/cGMP signaling, it is still not known which of NO's effects are mediated via NO-GC and thus cGMP, or alternatively, via pathways not involving cGMP.To address this point and to further investigate the physiological role of the enzyme and of the NO/cGMP signaling cascade in vivo, we generated an NO-GC-deficient mouse line. NO-GC is a heterodimer made up of two subunits, ␣ and ␤. Two isoforms are known to exist (␣ 1 ␤ 1 and ␣ 2 ␤ 1 ; ref. 15) in which the ␤ 1 subunit acts as the dimerizing partner for either ␣ subunit. ␣ subunits in the absence of the ␤ 1 subunit do not form dimers and are not catalytically active. Thus, deletion of the ␤ 1 subunit should completely eliminate NO-GC and yield a mouse line ...

In the vascular system, the receptor for the signaling molecule NO, guanylyl cyclase (GC), mediates smooth muscle relaxation and inhibition of platelet aggregation by increasing intracellular cyclic GMP (cGMP) concentration. The heterodimeric GC exists in 2 isoforms (a 1 -GC, a 2 -GC) with indistinguishable regulatory properties. Here, we used mice deficient in either a 1 -or a 2 -GC to dissect their biological functions. In platelets, a 1 -GC, the only isoform present, was responsible for NO-induced inhibition of aggregation. In aortic tissue, a 1 -GC, as the major isoform (94%), mediated vasodilation. Unexpectedly, a 2 -GC, representing only 6% of the total GC content in WT, also completely relaxed a 1 -deficient vessels albeit higher NO concentrations were needed. The functional impact of the low cGMP levels produced by a 2 -GC in vivo was underlined by pronounced blood pressure increases upon NO synthase inhibition. As a fractional amount of GC was sufficient to mediate vasorelaxation at higher NO concentrations, we conclude that the majority of NO-sensitive GC is not required for cGMP-forming activity but as NO receptor reserve to increase sensitivity toward the labile messenger NO in vivo.

The intracellular signalling molecule cGMP regulates a variety of physiological processes, and so the ability to monitor cGMP dynamics in living cells is highly desirable. Here, we report a systematic approach to create FRET (fluorescence resonance energy transfer)-based cGMP indicators from two known types of cGMP-binding domains which are found in cGMP-dependent protein kinase and phosphodiesterase 5, cNMP-BD [cyclic nucleotide monophosphate-binding domain and GAF [cGMP-specific and -stimulated phosphodiesterases, Anabaena adenylate cyclases and Escherichia coli FhlA] respectively. Interestingly, only cGMP-binding domains arranged in tandem configuration as in their parent proteins were cGMP-responsive. However, the GAF-derived sensors were unable to be used to study cGMP dynamics because of slow response kinetics to cGMP. Out of 24 cGMP-responsive constructs derived from cNMP-BDs, three were selected to cover a range of cGMP affinities with an EC50 between 500 nM and 6 microM. These indicators possess excellent specifity for cGMP, fast binding kinetics and twice the dynamic range of existing cGMP sensors. The in vivo performance of these new indicators is demonstrated in living cells and validated by comparison with cGMP dynamics as measured by radioimmunoassays.

The signaling molecule nitric oxide (NO) mediates many of its effects by the stimulation of soluble guanylyl cyclase (sGC). The activation process is initiated by high-affinity binding of NO to the enzyme's prosthetic heme group. Despite its poor sGC-activating properties, carbon monoxide (CO) has also been suggested as a physiological activator of sGC. Recently, we have shown that the substance YC-1, a benzyl indazole derivative, stimulates sGC by 10-fold (independently of NO) potentiates the stimulatory effect of NO, and turns CO into a potent activator of sGC. In the present study, we show that activation of sGC by protoporphyrin IX, a ligand-independent activator, was potentiated by YC-1, yet a shift of the concentration-response curve as seen with NO and CO was not observed. YC-1 slowed down the dissociation rates for NO and CO from the activated enzyme as monitored by cGMP accumulation after addition of the NO and CO scavenger oxyhemoglobin. A direct interaction of YC-1 with the heme group can be ruled out because YC-1 did not change the Soret absorption of basal or stimulated sGC and, in addition, still bound to the heme-depleted enzyme. Together, our results indicate that YC-1 increases the maximal catalytic rate and sensitizes the enzyme toward its gaseous activators by binding to an allosteric site on sGC molecules, thereby reducing the ligand dissociation rate from the heme group.