Catalytic Conversion of L-Arginine to Nitrate by Platinum Electrodes

Abstract

Platinum electrodes (PLE) have been used recently to study the physiologic effects of the enzymatic conversion of L-arginine (L-arg) to nitric oxide (NO) by nitric oxide synthase (NOS). We sought to determine if PLE alone could catalytically convert L-arg to NO without NOS. Accordingly, NO−2 + NO−3 levels (NOx) were measured by HPLC from a physiologic Tyrode′s buffer in the presence and absence of electrical stimulation with PLE or silver chloride electrodes (SCE) for 10 min (n = 6 for each condition). PLE stimulated at 1Hz produced 24 ± 0.7 and 15.4 ± 2.8 μM NOx from D-arg and L-arg (100mM) respectively. PLE+L-arg stimulated from 0 to 5 Hz produced increasing NOx (2.9 ± 0.27; 15.4 ± 2.8; 19.7 ± 4; 32 ± 5; 37 ± 6.2; 43 ± 7 μM). SCE+L-arg showed no increase in NOx above background. The addition of 1% BSA to the Tyrode′s buffer further increased NOx levels. NO−2 levels were undetectable, indicating all NOx levels were NO−3. We conclude that PLE can catalytically convert L-Arg to NO−3 via electron transfer without NOS.