Tyrosyl free radicals, production

Other very convincing evidences for free radical-mediated mechanism of decomposition and reactions of peroxynitrite and nitrosoperoxocarboxylate were demonstrated by Lehnig [140] with the use of CIDNP technique. This technique is based on the effects observed exclusively for the products of free radical reactions their NMR spectra exhibit emission characterizing a radical pathway of their formation. Lehnig has found the enhanced emission in the 15N NMR spectra of N03- formed during the decomposition of both peroxynitrite and nitrosoperoxocarboxylate. This fact indicates that N03- was formed from radical pairs [ N02, H0 ] and [ N02, C03 ]. Emission was also observed in the reaction of both nitrogen compounds with tyrosine supposedly due to the formation of radical pair [ N02, tyrosyl ]. 

Synthesis and clearance of free radicals are very active in the thyroid. Synthesis of thyroid hormones requires oxidation of iodine and iodination of tyrosyl in thy-roglobulin, wherein TPO and H2O2 synthesis systems are involved. Normally, the synthesis and clearance of H2O2 are in dynamic equilibriiim, but as H2O2 and other free radicals are over-produced or accumulated, cellular and mitochondrial membrane undergo lipid peroxidation, and finally necrosis and apoptosis. While in iodine deficiency, chronic TSH stimulation increases the production of H2O2, which results in oxidative damage of the thyroid. 

They observed specific inactivation of the B1 subunit of the E. coli enzyme, the production of free base and chloride, the irreversible modification of protein sulfhydryl groups, and the formation of a new chromophoric absorbance at 320 nm. The tyrosyl radical was not quenched following inactivation, and in this original report a new phosphorus-containing sugar was observed and tentatively identified as 2-deoxyribose 5-diphosphate. Furthermore, inactivation with [ C1]-, [a- P]-, or [5- H]ClCDP did not lead to radiolabeled protein. 

---