INTERACTION BETWEEN PEROXYNITRITE AND L-CYSTEINE - EFFECTS ON RAT AORTA

In rings of rat aorta previously exposed to peroxynitrite (1 mM), L-cy steine and its analogues containing, but not those lacking, a thiol gr oup produced a powerful transient relaxation. This relaxation is likel y to result from the release of nitric oxide from a nitrated/nitrosate d compound formed following reaction of peroxynitrite. with a componen t of the tissue or bathing medium. Furthermore, when peroxynitrite was pre-mixed with L-cysteine a new relaxant species was formed. Analogue s of L-cysteine with a free thiol reacted with peroxynitrite to form s pecies with similar relaxant potencies. Analogues lacking a thiol form ed products with relaxant activity, but less than with L-cysteine. Ana logues with a free amino but no thiol or carboxylic functions formed p roducts with potencies similar to those lacking only the thiol. If the amino is substituted and the thiol removed, no relaxant activity was generated. Thus, peroxynitrite reacts with L-cysteine to form a novel relaxant whose activity derives mainly from formation of its S-nitroso thiol, with a lesser component perhaps from an N-nitroso derivative. ( C) 1998 Elsevier Science B.V.