Recent reports have shown the presence of a ouabain-like inhibitor of Na+/K+-ATPase in humans. We have purified a bovine hypothalamic Na+/K+-ATPase inhibitory factor (HIF) by using affimity chromatography combined with HPLC. This inhibitor has a molecular weight of 584 as determined by ion-spray mass spectrometry, making it isobaric with ouabain. Glycosidase treatment or acid hydrolysis of HIF released only L-rhamnose, the hexose isomer found in ouabain, as detected by chiral GC/MS. Additionally, enzymatically generated desrhamnosyl HIF was found to have a molecular weight of 438, as does ouabagenin, the aglycone of ouabain. HIF and its aglycone were indistinguishable from ouabain and ouabagenin, respectively, by reversed-phase HPLC retention times. However, derivatization with naphthoylimidazole followed by HPLC revealed different retention times for naphthoylation products of HIF and ouabain. Subsequent CD spectroscopy on isolated naphthoylation products of HIF and ouabain confirmed that they were different. This study provides chromatographic and spectroscopic evidence that ouabain and HIF are isomeric cardenolides. The structural difference is presumed to account for the significant differences in biological properties observed for HIF and ouabain.The search for an endogenous inhibitor of Na+/K+-ATPase has been supported by the occurrence of digitalis-like cardiotonic steroids in plants and the presence of a highly conserved binding site for ouabain in mammalian tissues (1). Obstacles faced in attempts to identify such endogenous inhibitors have included the very low concentrations present in mammals and the difficulty ofobtaining stringently purified samples for analysis (2,3). Hamlyn and associates (4, 5) described a ouabain-like inhibitor of Na+/K+-ATPase from human plasma that was indistinguishable from ouabain ( Fig. 1, structure 1) by several criteria including mass spectrometry, immunoreactivity, and biological assays. Their results raised interesting speculation about the ability of humans to synthesize ouabain, previously known only as a plant product. Both portions of ouabain, specifically the highly functionalized steroid ouabagenin (Fig. 1, structure 2) and the sugar L-rhamnose (structure 3), are unprecedented in mammalian biosynthesis. Outside of the plant kingdom, only cardiotonic steroidal aglycones have been isolated from toads (6). In the present study, a Na+/K+-ATPase inhibitor from bovine hypothalamus (7) was purified by an enzyme affinity method coupled with preparative HPLC steps. Microanalytical methods were developed to directly compare the affinitypurified hypothalamic inhibitory factor (HIF) with authentic ouabain. Both HIF and ouabain were shown to have identicalThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. molecular weights and to yield L-rhamnose and isobaric aglycones upon hydrolysis. The stereochemistry of th...
For the past decade the immune system has been exploited as a rich source of de novo catalysts. Catalytic antibodies have been shown to have chemoselectivity, enantioselectivity, large rate accelerations, and even an ability to reroute chemical reactions. In many instances catalysts have been made for reactions for which there are no known natural or man-made enzymes. Yet, the full power of this combinatorial system can only be exploited if there was a system that allows for the direct selection of a particular function. A method that allows for the direct chemical selection for catalysis from antibody libraries was so devised, whereby the positive aspects of hybridoma technology were preserved and re-formatted in the filamentous phage system to allow direct selection of catalysis. This methodology is based on a purely chemical selection process, making it more general than biologically based selection systems because it is not limited to reaction products that perturb cellular machinery.
The coronavirus disease 2019 (COVID-19) pandemic caused by 2019 novel coronavirus (2019-nCoV) has been a crisis of global health, whereas the effective vaccines against 2019-nCoV are still under development. Alternatively, utilization of old drugs or available medicine that can suppress the viral activity or replication may provide an urgent solution to suppress the rapid spread of 2019-nCoV. Andrographolide is a highly abundant natural product of the medicinal plant, Andrographis paniculata , which has been clinically used for inflammatory diseases and anti-viral therapy. We herein demonstrate that both andrographolide and its fluorescent derivative, the nitrobenzoxadiazole-conjugated andrographolide (Andro- NBD), suppressed the main protease (M pro ) activities of 2019-nCoV and severe acute respiratory syndrome coronavirus (SARS-CoV). Moreover, Andro-NBD was shown to covalently link its fluorescence to these proteases. Further mass spectrometry (MS) analysis suggests that andrographolide formed a covalent bond with the active site Cys 145 of either 2019-nCoV M pro or SARS-CoV M pro . Consistently, molecular modeling analysis supported the docking of andrographolide within the catalytic pockets of both viral M pro s. Considering that andrographolide is used in clinical practice with acceptable safety and its diverse pharmacological activities that could be beneficial for attenuating COVID-19 symptoms, extensive investigation of andrographolide on the suppression of 2019-nCoV as well as its application in COVID-19 therapy is suggested.
Probes that react specifically with hydrogen peroxide to release chromophoric or fluorescent reporter groups were designed and synthesized.
[structure: see text] A new synthetic route was developed for the preparation of activity probe 1 for beta-glucosidase in this study. The key glycosidation step begins with benzyl p-hydroxyphenylacetate. Benzylic functionalization for the construction of the trapping device was achieved at later stages. Probe 1 was shown to be able to label the target enzyme. This cassette-like design offers great flexibility for future alterations. It would allow the synthetic scheme to expand to other glycosidase probes with different linker/reporter combinations.
The specific, high affinity binding of plant-derived digitalis glycosides by the mammalian sodium and potassium transporting adenosine triphosphatase (Na,K-ATPase, or sodium pump), a plasma membrane enzyme with critical physiological importance in mammalian tissues, has raised the possibility that a mammalian analog of digitalis might exist. We previously isolated and structurally characterized from bovine hypothalamus a novel isomer of the plant glycoside, ouabain, which differs structurally only in the attachment site and/or the stereochemistry of the steroid moiety [Tymiak et al. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 8189-8193]. Hamlyn and co-workers reported a molecule purified from human plasma which by mass spectrometry could not be distinguished from plant ouabain [Hamlyn et al. (1991) Proc. Natl. Acad. Sci. U.S.A. 88, 6259-6263]. Since rhamnoside cardiotonic steroids are not known as natural products from mammalian sources, it became important to compare these two pure isolates to determine if the same or structurally distinct compounds has been found. Our results indicate that the human and bovine Na,K-ATPase-inhibitors are identical, but different from plant ouabain. This supports the notion that the human sodium pump may be under specific physiological regulation by a mammalian analog of the digitalis glycosides.
Two mechanism-based activity probes, adopting a cassette-like design, for protein tyrosine phosphatases (PTPs) were synthesized. Both probes carry a phosphate group that serves as the recognition head for the target PTPs but differ in their reporter groups; probe LCL-1 uses a dansyl fluorophore, while LCL-2 has a biotin reporter group. LCL-1 and LCL-2 are specifically activated by phosphatase, leading to its covalent labeling, as exemplified with PTP-1B. However, they show no activation with other classes of hydrolases, including trypsin and beta-galactosidase. LCL-1 and LCL-2 thus represent the first example of class-selective probes for phosphatases.
To facilitate precatalyst recovery and reuse, we have developed a fluorous, oxime-based palladacycle 1 and demonstrated that it is a very efficient and versatile precatalyst for a wide range of carbon-carbon bond formation reactions (Suzuki-Miyaura, Sonogashira, Stille, Heck, Glaser-type, and Kumada) in either aqueous or organic medium under microwave irradiation. Palladacycle 1 could be recovered through F-SPE in various coupling reactions with recovery ranging from 84 to 95% for the first cycle. Inductively coupled plasma optical emission spectrometry (ICP-OES) analyses of the Pd content in the crude product from each class of transformation indicated extremely low levels of leaching and the palladacycle could be reused four to five times without significant loss of activity.
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