Correlation of chemical structure to biological function in nitric oxide-equivalents.

摘要

Nitric oxide (NO) participates in a vast number of physiological and pathological processes. Interestingly, the redox states of NO appear to control the activity exhibited in many biological systems. The apparent toxicity and short half-life of aqueous NO have suggested the presence of congeners which liberate bioactive NO species. These species have been termed "NO-equivalents" indicating their relationship to organic ideology.;Optical and non-optical spectroscopies have been used to correlate physical structure to biological function using two bioassays: smooth muscle relaxation and platelet inhibition. Two general types of NO-equivalents were profiled: covalently-NO-modified functional groups and NO-metal complexes (dinitrosoiron and mononitrosoiron complexes).;NO preferentially nitros(yl)ates thiols, alcohols, amines and then, finally, carbon substrates. Modification of these groups appears to be dependent upon the NO source type and the presence of other reactive functionalities. S-nitrosylation appears to be the most likely mode of transient NO-modification in vivo. To this end, RS;The identity of covalently-modified NO-equivalents was investigated via NMR, IR, and UV/Visible spectroscopies. A system of identification of several covalently-modified functionalities was developed through the use of isotopic labels and a combination of ;Dinitrosoiron complexes (DNICs) were characterized using EPR and ESEEM (Electron Spin Echo Envelope Modulation) to determine physical properties in vitro and their relation to in vivo processes. Results indicate DNICs are stable at physiologically-relevant pH values and can be formed under limiting conditions not previously utilized by investigators. Several novel spectra have been catalogued. Protein-DNIC interactions have been investigated previously but not in a manner as direct and precise as ESEEM. The effect of mercury on the DNICs was also investigated. Mercury(II) is often utilized as a method to assay free thiol. Mercury is shown by EPR spectroscopy to complex DNICs, thus challenging the validity of Hg-containing thiol assays.;Identification of NO activity in vivo and ex vivo was investigated utilizing EPR spin-trapping. The injection of a dithiol (DETC) and iron allows the formation of a paramagnetic complex in tissues producing NO. NO;The involvement of NO in biologic processes has necessitated the rigorous investigation of the correlation of physical composition and biological function in NO-equivalents. Experimental results indicate a tight correlation between structure and function in these compounds. Methods presented herein allow the study of the physical relationships discussed for in vitro and ex vivo systems.