Chapter 2 - DNICs: Physico-chemical properties and their observations in cells and tissues

Abstract

This chapter discusses the physico-chemical properties of dinitrosyl-iron complexes (DNICs). DNICs with thiol-containing ligands were discovered in cells and tissues with EPR spectroscopy. At room temperature, the protein-bound DNICs may be distinguished easily from their low-molecular-weight analogs. At this temperature, the EPR spectrum from protein-bound DNIC retains the shape of a powder spectrum as would be recorded in frozen solution at low temperature (77 K). In contrast, the low-molecular DNICs are rapidly tumbling and show a motionally narrowed isotropic line with a half-width of 0.7 mT and resolved 13-component hyperfine structure (HFS). The L-arginine-dependent formation of DNIC has been demonstrated in various cultured cells and tissues expressing inducible, high output, NO synthase activity. These presently include macrophages, fibroblasts, hepatocytes, vascular smooth muscle cells, isolated human islets of Langerhans, isolated rat aorta, different types of tumor cells (all treated with lipopolysaccharides and/or cytokines in vitro), as well as liver of mice treated with Corynebacterium parvum, murine tumor transplants, and rat heart allografts in vivo. Formation of DNIC via constitutive NO synthase was also demonstrated in isolated porcine endothelial cells stimulated with bradykinin or the ionophore A23187. The consideration of physico-chemical features of DNIC with thiol-containing ligands demonstrates that they can function in cells and tissues as a donor of neutral and ionized NO molecules. Besides that they can deliver Fe(NO)2 groups which can influence the activity of enzymes and proteins by binding with their functionally active thiol groups. DNICs are stable enough to ensure stabilization and transport of NO and NO+ thereby ensuring both their autocrynic and paracrynic functions.