Cell signaling entails a host of post-translational modifications of effector-proteins. These modifications control signal transmission by regulating the activity, localization or half-life of the effector-protein. Prominent oxidative modifications induced by cell-signaling reactive oxygen species (ROS) are cysteinyl modifications such as S-nitrosylation, sulfenic acid and disulfide formation. Disulfides protect protein sulfhydryls against oxidative destruction and simultaneously influence cell signaling by engaging redox-regulatory sulfhydryls in effector-proteins. The types of disulfides implicated in signaling span (1) protein S-glutathionylation, e.g. as a novel mode of Ras activation through S-glutathionylation at Cys-118 in response to a hydrogen-peroxide burst, (2) intra-protein disulfides, e.g. in the regulation of the stability of the protein phosphatase Cdc25C by hydrogen-peroxide, (3) inter-protein disulfides, e.g. in the hydrogen peroxide-mediated inactivation of receptor protein-tyrosine phosphatase α (RPTPα) by dimerization and (4) protein S-cysteaminylation by cystamine. Cystamine is a byproduct of pantetheinase-catalyzed pantothenic acid recycling from pantetheine for biosynthesis of Coenzyme A (CoA), a ubiquitous and metabolically indispensable cofactor. Cystamine inactivates protein kinase C-ε (PKCε), γ-glutamylcysteine synthetase and tissue transglutaminase by S-cysteaminylation-triggered mechanisms. The importance of protein S-cysteaminylation in signal transmission in vivo is evident from the ability of cystamine administration to rescue the intestinal inflammatory-response deficit of pantetheinase knockout mice. These mice lack the predominant epithelial pantetheinase isoform and have sharply reduced levels of cystamine/cysteamine in epithelial tissues. In addition, intraperitoneal administration of cystamine significantly delays neurodegenerative pathogenesis in a Huntington's disease mouse model. Thus, cystamine may serve as a prototype for the development of novel therapeutics that target effector-proteins regulated by S-cysteaminylation.