3). genetic and pharmacological analyses, read out as perturbation of specific equilibria within the SNO circuitry. The growing picture of NO biology entails equilibria among potentially thousands of different SNOs, governed by denitrosylases and nitrosylases. Thus, to elucidate the operation and effects of S-nitrosylation in cellular contexts, studies should consider the tasks of SNO-proteins as K-Ras G12C-IN-2 both focuses on and transducers of S-nitrosylation, functioning relating to enzymatically governed equilibria. multiple chemical routes that formally entail a one-electron oxidation, including reaction of NO with thiyl radical, transfer of the NO group from metal-NO complexes to Cys thiolate, or reaction of Cys thiolate with nitrosating varieties generated by NO auto-oxidation, exemplified by dinitrogen trioxide (N2O3) (60). However, the emerging evidence favors a primary part for metalloproteins in catalyzing S-nitrosylation (5, 26, 61, 119, 165), including under both aerobic and anaerobic conditions. The NO group can then transfer between donor and acceptor Cys thiols trans-S-nitrosylation (198), which likely functions as a main mechanism for S-nitrosylation in physiological settings. S-nitrosylation happens both in proteins, generating S-nitroso-proteins (SNO-proteins), and in low-molecular-weight (LMW) thiols, including glutathione (GSH) and coenzyme A (CoA), generating S-nitrosoglutathione (GSNO) and S-nitroso-coenzyme A (SNO-CoA), respectively (2, 21). Protein and LMW-SNOs exist in thermodynamic equilibria, which are governed by the removal of SNO-proteins by SNO-protein denitrosylases (namely thioredoxin [Trx] 1/2 and thioredoxin-related protein of 14?kDa [Trp14]) or of LMW-SNOs by GSNO and SNO-CoA metabolizing activities (Fig. 1). In effect, NO-based transmission transduction is definitely displayed by equilibria between LMW-SNOs and protein SNOs, and between SNO-proteins linked by transnitrosylation. Enzymatic governance of these equilibria, therefore, provides a basis for the rules of NO-based transmission transduction. Open in a separate windowpane FIG. 1. Coupled, dynamic equilibria that govern protein S-nitrosylation are controlled by enzymatic denitrosylases. (A) SNO-proteins are in equilibrium with LMW-SNOs K-Ras G12C-IN-2 and may further participate in protein-to-protein transfer of the NO group (trans-S-nitrosylation) to subserve NO-based signaling. (B) Transnitrosylation by both recognized LMW-SNOs (G, glutathione; CoA, coenzyme A; Cys, cysteine) and SNO-proteins will result in distinct units of SNO-proteins that mediate specific SNO signaling cascades. (C) Distinct enzymatic denitrosylases regulate the coupled equilibria that confer specificity to SNO-based signaling. These include GSNORs and SNO-CoA reductases, which regulate protein S-nitrosylation by GSNO and SNO-CoA, respectively. These LMW-SNOs are in equilibrium with cognate SNO-proteins. In contrast, Trxs directly denitrosylate RH-II/GuB SNO-proteins. The reaction techniques illustrated are detailed in the Enzymatic Denitrosylation section. GSNO, S-nitrosoglutathione; GSNORs, GSNO reductases; LMW-SNOs, low-molecular-weight S-nitrosothiol; NO, nitric K-Ras G12C-IN-2 oxide; SNO, S-nitrosothiol; SNO-CoA, S-nitroso-coenzyme A; SNO-protein, S-nitroso-protein; Trx, thioredoxin. SNO Specificity It is well established that protein S-nitrosylation exhibits impressive spatiotemporal specificity in the focusing on of protein Cys residues (44, 76, 97). Physiological amounts of NO typically target one or few Cys within a protein and this is sufficient to alter protein function and connected physiology or pathophysiology (39, 77, 166). It has emerged as a general rule that S-nitrosylation and alternate S-oxidative modifications, in particular those mediated by reactive oxygen varieties, most often target independent populations of Cys and, whether the same or different Cys are targeted, exert disparate practical effects (67, 165). Therefore, proteomic analyses of Cys modifications have exposed that, under physiological conditions, there is little overlap between different redox-based Cys modifications (45, 67). Functional specificity is definitely well illustrated in the case of the.