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S Behrends

Publications and source records attributed to S Behrends.

At least 55 records · Page 3Linked to original sources
PubMed1996

Characterization of 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one as a heme-site inhibitor of nitric oxide-sensitive guanylyl cyclase.

Nitric oxide (NO) binds with high affinity to the heme of soluble guanylyl cyclase (sGC), resulting in accumulation of the second messenger cGMP in many biological systems. 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) was recently described as potent and selective inhibitor of sGC, providing an invaluable tool with which to settle the function of the cGMP pathway in NO-mediated signal transduction [Mol. Pharmacol. 48:184-188 (1995)]. The present study investigated the mechanism of ODQ-induced inhibition of purified bovine lung sGC. The drug induced a rightward shift of the concentration-response curves recorded with two different NO donors and a reduction of maximal sGC activity, pointing to a mixed type of inhibition. The time course of NO-stimulated sGC activity determined in the presence of 0.3 microM ODQ showed that the inhibitory effect was time-dependent (half-time approximately 3 min) and virtually complete after about 10 min. The cyclase did not recover from ODQ-induced inhibition upon extensive dilution, pointing to an apparently irreversible inactivation of the enzyme by the quinoxalin. Light absorbance spectroscopy showed that ODQ (0.3 mM) induced a shift of the Soret band of the heme from 431 nm to 393 nm, indicating that ODQ oxidizes the ferrous form of the enzyme to the ferric species, which is though to exhibit only poor NO sensitivity. Together, our results suggest that inhibition of sGC by ODQ is NO-competitive and results in an apparently irreversible oxidation of the prosthetic heme group.

Animals↗
PubMed1995

A variant of the alpha 2 subunit of soluble guanylyl cyclase contains an insert homologous to a region within adenylyl cyclases and functions as a dominant negative protein.

A variant of the alpha 2 subunit of soluble guanylyl cyclase (alpha 2i) containing 31 additional amino acids was identified in a number of cell lines and tissues. The in-frame sequence of the insert was within the proposed catalytic domain of guanylyl cyclases and was homologous to a region within the putative catalytic domain of adenylyl cyclases. Messenger RNA for the new variant was detected in some but not all cell lines and tissues expressing the alpha 2 subunit. The novel form, as well as the alpha 2 subunit lacking the insert, were coexpressed with the beta 1 subunit in Sf9 and COS-7 cells; alpha 2/beta 1 coexpression yielded a NO-sensitive recombinant protein, whereas the coexpressed alpha 2i/beta 1 subunits exhibited no guanylyl or adenylyl cyclase activities. Because both subunits (alpha 2i/beta 1) copurified, the novel variant retains its ability to heterodimerize. In coexpression experiments, the alpha 2i subunit competed with the alpha 2 subunit for dimerization with the beta 1 subunit, thereby reducing alpha 2/beta 1-catalyzed guanylyl cyclase activity. These data show that the novel variant functions as a dominant negative protein and that post-transcriptional mRNA processing represents a potential mechanism for regulation of NO-sensitive guanylyl cyclase activity.

Adenylyl Cyclases↗