SALIVARY THIOL OXIDASE ACTIVITY OF RHODNIUS-PROLIXUS

Cysteine and other thiol compounds can accelerate the unloading of nit ric oxide (NO) from salivary nitrosyl-nitrophorins of the blood suckin g bug Rhodnius prolixus. The dependence of NO unloading on cysteine co ncentration is biphasic, showing a maximum between 0.5 and 1 mM cystei ne, The proposed mechanism of action for the unloading is a series of reactions where cysteine (at low concentrations) reacts with the heme group of nitrophorins to form cystine and superoxide, The superoxide t hen reacts,vith NO to form peroxynitrite, which decays to a mixture of nitrite and nitrate anions, At high cysteine concentrations, cysteine is converted to cystine and H2O and thus NO removal of NO from nitrop horins is observed, The thiol oxidase activity of Rhodnius nitrophorin s is similar to that observed before in plant peroxidases [Pichorner e t al., Phytochemistry 31, 3371 (1992)]. The possible physiological sig nificance of this reaction to probing and feeding by R. prolixus is di scussed. Copyright (C) 1996 Elsevier Science Ltd